MEDICATION-INDUCED BLOOD DYSCRASIAS
Etiology And Disease Types
Jassin M. Jouria, MD
Dr. Jassin M. Jouria is a medical doctor, professor of academic medicine, and medical author. He graduated from Ross University School of Medicine and has completed his clinical clerkship training in various teaching hospitals throughout New York, including King’s County Hospital Center and Brookdale Medical Center, among others. Dr. Jouria has passed all USMLE medical board exams, and has served as a test prep tutor and instructor for Kaplan. He has developed several medical courses and curricula for a variety of educational institutions. Dr. Jouria has also served on multiple levels in the academic field including faculty member and Department Chair. Dr. Jouria continues to serves as a Subject Matter Expert for several continuing education organizations covering multiple basic medical sciences. He has also developed several continuing medical education courses covering various topics in clinical medicine. Recently, Dr. Jouria has been contracted by the University of Miami/Jackson Memorial Hospital’s Department of Surgery to develop an e-module training series for trauma patient management. Dr. Jouria is currently authoring an academic textbook on Human Anatomy & Physiology.
Abstract
Although drug-induced hematologic disorders are less common than other types of adverse reactions, they are associated with significant morbidity and mortality. Some agents, such as hemolytics, cause predictable hematologic disease, but others induce idiosyncratic reactions not directly related to the drug’s pharmacology. The most important part of managing hematologic disorders is the prompt recognition that a problem exists. The main mechanisms to manage hematologic disorders include vigilance to observe signs and symptoms indicating a blood disorder and patient education of the warning symptoms to alert them of the need to report a condition to their primary care provider or an emergency health team.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 1 Continuing Nursing Education Course Director & Planners
William A. Cook, PhD, Director, Douglas Lawrence, MA, Webmaster,
Susan DePasquale, MSN, FPMHNP-BC, Lead Nurse Planner
Policy Statement
This activity has been planned and implemented in accordance with the policies of NurseCe4Less.com and the continuing nursing education requirements of the American Nurses Credentialing Center's Commission on Accreditation for registered nurses. It is the policy of NurseCe4Less.com to ensure objectivity, transparency, and best practice in clinical education for all continuing nursing education (CNE) activities.
Continuing Education Credit Designation
This educational activity is credited for 4 hours. Nurses may only claim credit commensurate with the credit awarded for completion of this course activity.
Pharmacology content is 0.5 hours (30 minutes).
Statement of Learning Need
Clinicians need to know how to manage the risk of hematologic disorders induced by medication. Understanding the risk, recognizing the signs and symptoms that may indicate a blood disorder, and being skilled in how to educate the patient are essential knowledge needs of clinicians to ensure patients, caregivers and health teams are able to recognize the warning symptoms of hematologic disorders.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 2 Course Purpose
To provide nurses and health team associates with knowledge about medication-induced dyscrasias to better recognize, treat, and educate patients, caregivers and all health team members on acute and long-term management.
Target Audience Advanced Practice Registered Nurses and Registered Nurses
(Interdisciplinary Health Team Members, including Vocational Nurses and Medical Assistants may obtain a Certificate of Completion)
Course Author & Director Disclosures
Jassin M. Jouria, MD, William S. Cook, PhD, Douglas Lawrence, MA
Susan DePasquale, MSN, FPMHNP-BC – all have no disclosures
Acknowledgement of Commercial Support
There is no commercial support for this course.
Activity Review Information
Reviewed by Susan DePasquale, MSN, FPMHNP-BC
Release Date: 5/19/2016 Termination Date: 5/19/2019
Please take time to complete a self-assessment of knowledge, on page 4, sample questions before reading the article.
Opportunity to complete a self-assessment of knowledge learned will be provided at the end of the course. nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 3 1. ______is a lowered threshold to the normal pharmacological action of a drug.
a. Dyscrasia b. Intolerance c. Hypersensitivity d. Idiosyncrasy
2. True or False: Idiosyncrasy differs from intolerance in that it is not an exaggeration of the normal response; it is an abnormal response per se.
a. True b. False
3. The development of corneal opacities and retinal damage in patients treated with chloroquine as an antimalarial or for arthritis and amebiasis is an example of a drug
a. side effect. b. intolerance. c. hypersensitivity. d. overdosage.
4. The principal ions necessary for normal cell function include calcium, sodium, potassium, ______, magnesium, and hydrogen.
a. albumin b. bilirubin c. chloride d. heme
5. The main protein constituent of plasma is ______, which is the most important component in maintaining osmotic pressure.
a. intrinsic factor (IF) b. bilirubin c. heme d. albumin
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 4 Introduction
Hematologic disorders have long been a potential risk of modern pharmacotherapy. Although drug-induced hematologic disorders are less common than other types of adverse reactions, they are associated with significant morbidity and mortality. Some agents, such as hemolytics, cause predictable hematologic disease, but others induce idiosyncratic reactions not directly related to the drug’s pharmacology. The most important part of management of a hematologic disorder is the prompt recognition when a problem exists. This is done by two mechanisms: firstly, vigilance for signs and symptoms that may indicate a blood disorder; and, secondly, patient education about the warning symptoms that should alert them to the need to urgently contact their medical provider or emergency services if a prompt medical appointment is not possible. This two-part course series discusses the link between modern pharmacotherapy and hematologic disorders and the identification and management of this risk.
Medication-Induced Hematologic Disease: An Overview
Some agents cause predictable hematologic diseases, such as antineoplastic medication, but others induce idiosyncratic reactions not directly related to the drug’s pharmacology. The most common drug-induced hematologic disorders include aplastic anemia, agranulocytosis, megaloblastic anemia, hemolytic anemia, and thrombocytopenia.
The incidence of idiosyncratic drug-induced hematologic disorders varies depending on the condition and the associated drug. Few epidemiologic studies have evaluated the actual incidence of these adverse reactions, but these reactions appear to be rare. Women are generally more susceptible than men to the hematologic effects of drugs. The incidence varies based on
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 5 geography, which suggests that genetic differences may be important determinants of susceptibility.
Drug-induced thrombocytopenia is the most common drug-induced hematologic disorder. Some reports of heparin-induced thrombocytopenia suggest as many as 5% of patients who receive heparin develop thrombocytopenia. The Berlin Case-Control Surveillance Study was conducted from 2000 to 2009 to assess the incidence and risks of drug- induced hematologic disorders. This evaluation found that almost 30% of all cases of blood dyscrasias were possibly attributable to drug therapy.
Although drug-induced hematologic disorders are less common than other types of adverse reactions, they are associated with significant morbidity and mortality. An epidemiologic study conducted in the United States estimated that 4,490 deaths were attributable to blood dyscrasias from all causes. Aplastic anemia was the leading cause of death followed by thrombocytopenia, agranulocytosis, and hemolytic anemia. Similar to most other adverse drug reactions, drug-induced hematologic disorders are more common in elderly adults than in the young; and, the risk of death also appears to be greater with increasing age.
Because of the seriousness of drug-induced hematologic disorders, it is necessary to track the development of these disorders to predict their occurrence and to estimate their incidence. Reporting during postmarketing surveillance of a drug is the most common method of establishing the incidence of adverse drug reactions. The MedWatch program supported by the Food and Drug Administration (FDA) is one such program. Many facilities have similar drug-reporting programs to follow adverse drug reaction trends and to determine whether an association between a drug and an adverse
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 6 drug reaction is causal or coincidental. In the case of drug-induced hematologic disorders, these programs can enable practitioners to confirm that an adverse event is indeed the result of drug therapy rather than one of many other potential causes; general guidelines are readily available.1
Adverse Drug Effect1,2
Blood dyscrasias are a rare, yet extremely serious, adverse effect of drug treatment. Outside of the more predictable bone marrow depression seen with cytotoxic and immunosuppressant agents, drugs in more common use have also been associated with blood disorders. Drug-induced blood disorders have also been the reason for withdrawal for a number of drugs, notably remoxipride in 1994. Although anecdotal reports of drug-induced blood disorders are common in the literature, they often have speculative mechanisms and questionable causality. The true incidence of drug-induced dyscrasias is therefore difficult to ascertain, but it is clear that they make a major contribution to the incidence of blood disorders.
In practice, drug-induced reactions can be difficult to avoid, but knowledge of the propensity of drugs to initiate such reactions does allow prescribers to be both vigilant for early signs of blood disorders and inform patients about signs and symptoms. Early recognition is crucial in mitigating the effects of these serious and sometimes fatal adverse effects. Dyscrasia, a word of Greek origin, means unwanted mixture and, as used herein, connotes a disorder of the blood caused by an undesirable effect of a drug. The undesirable effects of drugs may be divided into six categories: overdosage, intolerance, side effects, secondary effects, idiosyncrasy and hypersensitivity.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 7 Overdosage with any drug may produce serious ill effects which are usually predictable from animal experiments and which occur in direct relation to the total amount of drug administered; it may be absolute, the result of ignorance or error, or it may be relative. Impairment of excretion or destruction in the presence of disease of the kidney or liver may render a normal dose toxic though accumulation of the drug. Examples are the dangerous effect of a normal dose of morphine in the presence of hepatic damage, and the potentiation of digitalis action when an increase in the blood level of potassium co-exists.
Intolerance is a lowered threshold to the normal pharmacological action of a drug, and until recently was explained in terms of biological variation. Now, however, a more satisfactory explanation may be available on a biochemical basis. Side effects are therapeutically undesirable but inevitable effects of drug action. Examples are numerous, such as the masculinizing effect of androgen used for carcinoma of the breast, the osteoporosis and edema following the administration of cortisone to patients with rheumatoid arthritis, and the acoustic nerve damage due to streptomycin. Examples of unexpected and unpredictable side effects are the congenital deformities following the use of thalidomide in pregnancy, and the development of corneal opacities and retinal damage in patients treated with chloroquine as an antimalarial or for arthritis and amebiasis.
Secondary effects are the indirect consequences of primary drug action. They have become common since the introduction of antibiotics and include the development of avitaminosis due to interference with the normal flora of the gut, as well as super-infection by other organisms.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 8 Idiosyncrasy differs from intolerance in that it is not an exaggeration of the normal response; it is an abnormal response per se. It differs from hypersensitivity in that it does not depend on previous contact with the drug; it occurs when the drug is first administered. The clinical anaphylactoid reaction fits into this category of an inherent qualitatively abnormal response to a drug; this is exemplified by the sudden collapse and syncope that may follow the application of cocaine to the conjunctiva for the removal of a cinder.
Hypersensitivity is an antigen-antibody phenomenon in which the antibodies produced by previous contact with the foreign substance - chemical or biological, humoral or bound to fixed tissue - cause a reaction, which may be immediate or delayed. This mechanism is held by many to be involved in most of the common drug reactions, although an antigen-antibody reaction cannot often be demonstrated. Hypersensitivity reactions, it must be emphasized, occur in only a very small percentage of patients exposed to drugs. It is possible that idiosyncrasy may predispose certain individuals to such reactions; it is well known that those with an allergy are more likely to become candidates for other hypersensitizations than patients without a history of allergy.
Drug Effects on Bone Marrow2
The bone marrow performs the task of providing the body with a balanced supply of all circulating blood cells throughout life. Variability in demand for differing types of blood cells is provided by the self-renewing pluripotential stem cells, from which the fully mature cell lines such as erythrocytes, granulocytes, platelets, macrophages and lymphocytes arise. Drugs can have differing effects on the various cell types, at differing stages in cell development.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 9 Failure of stem cells leading to peripheral blood cytopenia is termed hypoplasia or aplasia. This can take two forms: aplastic anemia, due to damage sustained by the pluripotential stem cells, or single-cell pancytopenia, where damage is due to a specific committed cell line. Such diversity of effects leads to a wide spectrum of potential blood disorders depending on where and at what point in the production of the cell line the drug acts upon. The risk for individuals can also vary. The decline in the size of the hemopoietic bone marrow with age increases susceptibility. Certain blood disorders can be more linked to the sex of the individual, or to a genetic propensity to suffer the reaction.
Blood Composition and Signs of Disease3,4
Blood is composed of a liquid called plasma and of cellular elements, including leukocytes, platelets, and erythrocytes. The normal adult has about 6 liters of this vital fluid, which composes from 7% to 8% of the total body weight. Plasma makes up about 55% of the blood volume; about 45% of the volume is composed of erythrocytes, and 1% of the volume is composed of leukocytes and platelets. Variations in the quantity of these blood elements are often the first sign of disease occurring in body tissue. Changes in diseased tissue may be detected by laboratory tests that measure deviations from normal in blood constituents; hematology is primarily the study of the formed cellular blood elements.
The principal component of plasma is water, which contains dissolved ions, proteins, carbohydrates, fats, hormones, vitamins, and enzymes. The principal ions necessary for normal cell function include calcium, sodium, potassium, chloride, magnesium, and hydrogen. The main protein constituent of plasma is albumin, which is the most important component in maintaining osmotic pressure. Albumin also acts as a carrier molecule, nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 10 transporting compounds such as bilirubin and heme. Other blood proteins carry vitamins, minerals, and lipids. Immunoglobulins, synthesized by lymphocytes, and complement are specialized blood proteins involved in immune defense. The coagulation proteins responsible for hemostasis (arrest of bleeding) circulate in the blood as inactive enzymes until they are needed for the coagulation process. An upset in the balance of these dissolved plasma constituents can indicate a disease in other body tissues.
Blood plasma also acts as a transport medium for cell nutrients and metabolites; for example, the blood transports hormones manufactured in one tissue to target tissue in other parts of the body. Albumin transports bilirubin, the main catabolic residue of hemoglobin, from the spleen to the liver for excretion. Blood urea nitrogen, a nitrogenous waste product, is carried to the kidneys for filtration and excretion. Increased concentration of these normal catabolites can indicate either increased cellular metabolism or a defect in the organ responsible for their excretion. For example, in liver disease, the bilirubin level in blood increases because the liver is unable to function normally and clear the bilirubin. In hemolytic anemia, however, the bilirubin concentration can rise because of the increased metabolism of hemoglobin that exceeds the ability of a normal liver to clear bilirubin.
When body cells die, they release their cellular constituents into surrounding tissue. Eventually, some of these constituents reach the blood. Many constituents of body cells are specific for the cell’s particular function; thus, increased concentration of these constituents in the blood, especially enzymes, can indicate abnormal cell destruction in a specific organ. Blood cells are produced and develop in the bone marrow. This process is known as hematopoiesis. Undifferentiated hematopoietic stem cells (precursor cells) proliferate and differentiate under the influence of proteins that affect their
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 11 function (cytokines). When the cell reaches maturity, it is released into the peripheral blood.
Each of the three cellular constituents of blood has specific functions. Erythrocytes contain the vital protein hemoglobin, which is responsible for transport of oxygen and carbon dioxide between the lungs and body tissues. The five major types of leukocytes are neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Each type of leukocyte has a role in defending the body against foreign pathogens such as bacteria and viruses. Platelets are necessary for maintaining hemostasis. Blood cells circulate through blood vessels, which are distributed throughout every body tissue. Erythrocytes and platelets generally carry out their functions without leaving the vessels, but leukocytes diapedese (pass through intact vessel walls) to tissues where they defend against invading foreign pathogens.
Hematopoietic System
The adult hematopoietic system includes tissues and organs involved in the proliferation, maturation, and destruction of blood cells. These organs and tissues include the bone marrow, thymus, spleen, and lymph nodes. Bone marrow is the site of myeloid, erythroid, and megakaryocyte as well as early stages of lymphoid cell development. Thymus, spleen, and lymph nodes are primarily sites of later lymphoid cell development. Tissues in which lymphoid cell development occurs are divided into primary and secondary lymphoid tissue. The hematopoietic system is reviewed in this section with a summary of normal organ/gland and cell function and emphasis on how medication can adversely impact normal blood cell function as well as the treatment required when hematological disease states arise.5
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 12 Primary lymphoid tissues (bone marrow and thymus) are those in which T and B cells develop from nonfunctional precursors into cells capable of responding to foreign antigens (immunocompetent cells). Secondary lymphoid tissues (spleen and lymph nodes) are those in which immunocompetent T and B cells further divide and differentiate into effector cells and memory cells in response to antigens.
Bone Marrow
Blood-forming tissue located between the trabeculae of spongy bone is known as bone marrow. (Trabecula refers to a projection of bone extending from cortical bone into the marrow space; it provides support for marrow cells). This major hematopoietic organ is a cellular, highly vascularized, loose connective tissue. It is composed of two major compartments: the vascular and the endosteal. The vascular compartment is composed of the bone marrow arteries and veins, stromal cells, and hematopoietic cells. The endosteal compartment is primarily the site of bone remodeling but also contains hematopoietic stem cell (HSC).
Vasculature Supply of Bone Marrow
The vascular supply of bone marrow is served by two arterial sources, a nutrient artery and a periosteal artery, that enter the bone through small holes, the bone foramina. Blood is drained from the marrow via the central vein. The nutrient artery branches around the central sinus that spans the marrow cavity.
Arterioles radiate outward from the nutrient artery to the endosteum (the inner lining of the cortical bone), giving rise to capillaries that merge with capillaries from periosteal arteries to form sinuses within the marrow. The
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 13 sinuses, lined by single endothelial cells and supported on the abluminal side (away from the luminal surface) by adventitial reticular cells, ultimately gather into wider collecting sinuses, which open into the central longitudinal vein. The central longitudinal vein continues through the length of the marrow and exits through the foramen where the nutrient artery entered. Nerve fibers surrounding marrow arteries regulate blood flow into the bone marrow, which in turn controls hematopoietic progenitor release into the circulation.
The major arterial supply to the marrow is from periosteal capillaries and capillary branches of the nutrient artery that have traversed the bony enclosure of the marrow through the bone foramina. The capillaries join with the venous sinuses as they re-enter the marrow. The sinuses gather into wider collecting sinuses that then open into the central longitudinal vein (central sinus).
Bone Marrow Stroma
The bone marrow stroma (supporting tissue in the vascular compartment) provides a favorable microenvironment for sustained proliferation of hematopoietic cells, forming a meshwork that creates a three-dimensional scaffolding for them. Stromal cellular components also provide cytokines that regulate hematopoiesis. The stroma is composed of three major cell types: macrophages, reticular cells (fibroblasts), and adipocytes (fat cells).
Macrophages serve two major functions in the bone marrow: phagocytosis and secretion of hematopoietic cytokines (proteins secreted by a cell, which modulate the function of another cell). Macrophages phagocytose the extruded nuclei of maturing erythrocytes, B cells that have not differentiated properly, and differentiating cells that die during development. Some
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 14 macrophages serve as the center of the erythroblastic islands, as discussed in the section below on hematopoietic cells. Macrophages also provide many colony-stimulating factors (cytokines that stimulate the growth and development of immature hematopoietic cells) needed for the development of myeloid lineage cells. Macrophages stain acid phosphatase positive.
Reticular cells are located on the abluminal surface of the vascular sinuses and send long cytoplasmic processes into the stroma. They are an abundant source of CXCL12 (SDF-1), which is critical for maintaining an HSC pool in the marrow. These cells also produce reticular fibers, which contribute to the three-dimensional supporting network that holds the vascular sinuses and hematopoietic elements. The fibers can be visualized with light microscopy and after silver staining. Reticular cells are alkaline phosphatase positive.
Adipocytes are cells whose cytoplasm is largely replaced with a single fat vacuole. They differentiate from mesenchymal stem cells (MSCs), and their production is inversely proportional to osteoblast formation. MSCs are multipotent stromal cells that can differentiate into bone, cartilage, and fat cells. Adipocytes mechanically control the volume of bone marrow in which active hematopoiesis takes place. They also provide steroids and other cytokines that influence hematopoiesis and maintain osseous bone integrity. The proportion of bone marrow composed of adipocytes changes with age. For the first 4 years of life, nearly all marrow cavities are composed of hematopoietic cells, or red marrow. After 4 years of age, adipocytes or yellow marrow gradually replaces the red marrow in the shafts of long bones.
By the age of 25 years, hematopoiesis is limited to the marrow of the skull, ribs, sternum, scapulae, clavicles, vertebrae, pelvis, upper half of the
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 15 sacrum, and proximal ends of the long bones. The distribution of red:yellow marrow in these bones is about 1:1. The fraction of red marrow in these areas continues to decrease with aging. Osteoblasts and osteoclasts are found in the endosteum (internal surface of calcified bone). These cells can be dislodged during bone marrow biopsy and can be found in the specimen with hematopoietic cells.
Osteoblasts differentiate from MSCs; and, osteoclasts differentiate from HSCs. Osteoblasts are involved in the formation of calcified bone and produce cytokines that can positively or negatively regulate HSC activity. They are large cells (up to 30 mcM (μm) in diameter) that resemble plasma cells except that the perinuclear halo (Golgi apparatus) is detached from the nuclear membrane and, in Wright-stained specimens, appears as a light area away from the nucleus. In addition, the cytoplasm can be less basophilic, and the nucleus has a finer chromatin pattern than plasma cells. Osteoblasts are normally found in groups and are more commonly seen in children and in metabolic bone diseases. The cells are alkaline phosphatase positive.
Osteoclasts are cells related to macrophages that are involved in resorption and remodeling of calcified bone. Up to 100 mcM in diameter, they are even larger than osteoblasts. The cells are multinucleated, form from fusion of activated monocytes, and have granular cytoplasm that can be either acidophilic or basophilic. They resemble megakaryocytes except that the nuclei are usually discrete (whereas the megakaryocyte has a single, large multilobulated nucleus) and often contain nucleoli.
Hematopoietic Cells
These cells are arranged in distinct niches within the vascular compartment of the marrow cavity. Erythroblasts constitute 25–30% of the marrow cells
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 16 and are produced near the venous sinuses. They develop in erythroblastic islands composed of a single macrophage surrounded by erythroblasts in varying states of maturation. The macrophage cytoplasm extends out to surround the erythroblasts. During this close association, the macrophages regulate erythropoiesis by secreting various cytokines.
The least mature cells are closest to the center of the island, and the more mature cells are at the periphery. The location of leukocyte development differs depending on the cell type. Granulocytes are produced in nests close to the trabeculae and arterioles and are relatively distant from the venous sinuses. These nests are not quite as apparent morphologically as are erythroblastic islands.
Megakaryocytes are very large, polyploid cells (DNA content more than 2N) that produce platelets from their cytoplasm. They are located adjacent to the vascular sinus. Cytoplasmic processes of the megakaryocyte form long proplatelet processes that pinch off to form platelets. Lymphocytes are normally produced in lymphoid aggregates located near arterioles. Lymphoid progenitor cells can leave the bone marrow and travel to the thymus where they mature into T lymphocytes. Some remain in the bone marrow where they mature into B lymphocytes. Some B cells return to the bone marrow after being activated in the spleen or lymph node. Activated B cells transform into plasma cells, which can reside in the bone marrow and produce antibody.
Bone marrow stromal location of erythrocyte, granulocyte, platelet, and lymphocyte differentiation is essential to understand. The bone forms a rigid compartment for the marrow. Thus, any change in volume of the hematopoietic tissue, as occurs in many anemias and leukemias, must be
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 17 compensated for by a change in the space-occupying adipocytes. Normal red marrow can respond to stimuli and increase its activity to several times the normal rate. As a result, the red marrow becomes hyperplastic and replaces portions of the fatty marrow.
Bone marrow hyperplasia (an excessive proliferation of normal cells) accompanies all conditions with increased or ineffective hematopoiesis. The degree of hyperplasia is related to the severity and duration of the pathologic state. Acute blood loss can cause erythropoietic tissue to temporarily replace fatty tissue; severe chronic anemia can cause erythropoiesis to be so intense that it not only replaces fatty marrow but also erodes the bone’s internal surface.
In malignant diseases that invade or originate in the bone marrow, such as leukemia, proliferating abnormal cells can replace both normal hematopoietic tissue and fat. In contrast, the hematopoietic tissue can become inactive or hypoplastic (a condition in which the hematopoietic cells in bone marrow decrease). Fat cells then increase, providing a cushion for the marrow. Environmental factors such as chemicals and toxins can suppress hematopoiesis whereas other types of hypoplasia can be genetically determined. Myeloproliferative disease, which begins as a hypercellular disease, frequently terminates in a state of aplasia (absence of hematopoietic tissue in bone marrow) in which fibrous tissue replaces hematopoietic tissue.
Blood Cell Egress
Special properties of the maturing hematopoietic cell and of the venous sinus wall are important in migration of blood cells from the bone marrow to the circulation. These cells must migrate between reticular cells but through
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 18 endothelial cells to reach the circulation. As cell traffic across the sinus increases, the reticular cells contract, creating a less continuous layer over the abluminal sinus wall. When the reticular cell layer contracts, it creates compartments between the reticular cell layer and the endothelial layer where mature cells accumulate and can interact with sites on the sinus endothelial surface.
The new blood cell interacts with the abluminal endothelial membrane by a receptor-mediated process, forcing the abluminal membrane into contact with the luminal endothelial membrane. The two membranes fuse, and under pressure from the passing cell, they separate, creating a pore through which the hematopoietic cell enters the lumen of the sinus. These pores are only 2–3 mcM in diameter; thus, blood cells must have the ability to deform so that they can pass through the sinusoidal lining. Progressive increases in deformability and motility have been noted as granulocytes mature from the myeloblast to the segmented granulocyte stage, facilitating the movement of cells into the sinus lumen.
Many soluble factors are important in regulating the release of blood cells from bone marrow, including granulocyte-colony stimulating factor (G-CSF), granulocyte monocyte-colony stimulating factor (GM-CSF), and a large number of chemokines. Some of these molecules are used clinically to increase circulating granulocytes or release HSCs into the circulation to obtain granulocytes for transfusion or stem cells for transplantation.
Extramedullary Hematopoiesis
Hematopoiesis in the bone marrow is called medullary hematopoiesis. Extramedullary hematopoiesis denotes blood cell production in hematopoietic tissue other than bone marrow. In certain hematologic
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 19 disorders, when hyperplasia of the marrow cannot meet the physiologic blood needs of the tissues, extramedullary hematopoiesis can occur in the hematopoietic organs that were active in the fetus, principally the liver and spleen. Organomegaly frequently accompanies significant hematopoietic activity at these sites.
Thymus
The thymus is a lymphopoietic organ located in the upper part of the anterior mediastinum. It is a bilobular organ demarcated into an outer cortex and central medulla. The cortex is densely packed with small lymphocytes (thymocytes), cortical epithelial cells, and a few macrophages. The medulla is less cellular and contains more mature thymocytes mixed with medullary epithelial cells, dendritic cells, and macrophages.
The primary purpose of the thymus is to serve as a compartment in which T lymphocytes mature. Precursor T cells leave the bone marrow and enter the thymus through arterioles in the cortex. As they travel through the cortex and the medulla, they interact with epithelial cells and dendritic cells, which provide signals to ensure that T cells can recognize foreign antigen but not self-antigen. They also undergo rapid proliferation. Only about 3% of the cells generated in the thymus successfully exit the medulla as mature T cells; the rest die by apoptosis and are removed by thymic macrophages.
The thymus is responsible for supplying the T-dependent areas of lymph nodes, spleen, and other peripheral lymphoid tissue with immunocompetent T lymphocytes. The thymus is a well-developed organ at birth and continues to increase in size until puberty. After puberty, however, it begins to atrophy until old age when it becomes barely recognizable. Increased steroid levels beginning in puberty and decreased growth factor levels in adults may drive
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 20 this atrophy. The atrophy is characterized by reduced expression of a transcription factor (FOXN1) required for thymic epithelial cell differentiation. The atrophied thymus is still capable of producing some new T cells if the peripheral pool becomes depleted as occurs after the lymphoid irradiation that accompanies bone marrow transplantation.
Spleen
The spleen is located in the upper-left quadrant of the abdomen beneath the diaphragm and to the left of the stomach. After several emergency splenectomies were performed without causing permanent harm to the patients, it was recognized that the spleen was not essential to life. However, it does play a role in filtering foreign substances and old erythrocytes from the circulation, storage of platelets, and immune defense.
Architecture of the Spleen
Enclosed by a capsule of connective tissue, the spleen contains the largest collection of lymphocytes and macrophages in the body. These cells, together with a reticular meshwork, are organized into three zones: white pulp, red pulp, and the marginal zone. The white pulp, a visible grayish- white zone, is composed of lymphocytes and is located around a central artery. The area closest to the artery, which contains many T cells as well as macrophages and dendritic cells, is termed the periarteriolar lymphatic sheath (PALS). Peripheral to this area are B cells arranged into follicles (a sphere of B cells within lymphatic tissue).
Activated B cells are found in specialized follicular areas called germinal centers, which appear as lightly stained areas in the center of a lymphoid follicle. The germinal centers consist of a mixture of B lymphocytes, follicular dendritic cells, and phagocytic macrophages. The immune response is nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 21 initiated in the white pulp. In some cases of heightened immunologic activity, the white pulp can increase to occupy half the volume of the spleen (it is normally ≤20%). The marginal zone, a reticular meshwork containing blood vessels, macrophages, and specialized B cells, surrounds white pulp. This zone lies at the junction of the white pulp and red pulp and is important in initiating rapid immune responses to blood-borne pathogens and performing functions similar to that of the red pulp. The red pulp contains sinuses and cords.
The sinuses are dilated vascular spaces for venous blood. The pulp’s red color is caused by the presence of large numbers of erythrocytes in the sinuses. The cords are composed of masses of reticular tissue and macrophages that lie between the sinuses. The cords of the red pulp provide zones for platelet storage and destruction of damaged blood cells.
Spleen Blood Flow
The spleen is richly supplied with blood. It receives 5% of the total cardiac output, a blood volume of 300 mL/minute. Blood enters the spleen through the splenic artery, which branches into many central arteries. Vessel branches can terminate in the white pulp, red pulp, or marginal zone. Blood entering the spleen can follow either the rapid transit pathway (closed circulation) or the slow transit pathway (open circulation). The rapid transit pathway is a relatively unobstructed route by which blood enters the sinuses in red pulp from the arteries and passes directly to the venous collecting system. In contrast, blood entering the slow transit pathway moves sluggishly through a circuitous route of macrophage-lined cords before it gains access to the venous sinuses.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 22 Plasma in the cords freely enters the sinuses, but erythrocytes meet resistance at the sinus wall where they must squeeze through the tiny openings. This skimming of the plasma from blood cells sharply increases the hematocrit in the cords. Sluggish blood-flow and continued erythrocyte metabolic activity in the cords result in a splenic environment that is hypoxic, acidic, and hypoglycemic. Hypoxia and hypoglycemia occur as erythrocytes utilize available oxygen and glucose, and metabolic byproducts create the acidic environment.
Spleen Function
Blood that empties into the cords of the red pulp or the marginal zone takes the slow transit pathway, which is very important to splenic function including culling, pitting, and storing blood cells. The discriminatory filtering and destruction of senescent (aged) or damaged red cells by the spleen is termed culling. Cells entering the spleen through the slow transit pathway become concentrated in the hypoglycemic, hypoxic cords of the red pulp — a hazardous environment for aged or damaged erythrocytes. Slow passage through a macrophage-rich route allows the phagocytic cells to remove these old or damaged, less deformable erythrocytes before or during their squeeze through the 3 mcM pores to the venous sinuses. Normal erythrocytes withstand this adverse environment and eventually re-enter the circulation.
Pitting refers to the spleen’s ability to pluck out particles from intact erythrocytes without destroying them. Blood cells coated with antibody are susceptible to pitting by macrophages. The macrophage removes the antigen–antibody complex and the attached membrane. The pinched-off cell membrane can reseal itself, but the cell cannot synthesize lipids and proteins for new membrane due to its lack of cellular organelles. Therefore, extensive
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 23 pitting causes a reduced surface-area-to-volume ratio, resulting in the formation of spherocytes (erythrocytes that have no area of central pallor on stained blood smears). The presence of spherocytes on a blood film is evidence that the erythrocyte has undergone membrane assault in the spleen.
The white pulp and marginal zones of the spleen are important lines of defense in blood-borne infections because of their rich supply of lymphocytes and phagocytic cells (macrophages) and the slow transit circulation through these areas. Blood-borne antigens are forced into close contact with macrophages (functioning as antigen-presenting cells) and lymphocytes allowing for recognition of the antigen as foreign and leading to phagocytosis, T- and B-cell activation, and antibody formation.
The spleen’s immunologic function is probably less important in the well- developed adult immune system than in the still-developing immune system of the child. Young children who undergo splenectomy may develop overwhelming, often fatal, infections with encapsulated organisms such as Streptococcus pneumonia and Hemophilus influenza. This can also be a rare complication of splenectomy in adults. The loss of the marginal zone can be especially important in this regard. The red pulp cords of the spleen act as a reservoir for platelets, sequestering approximately one-third of the circulating platelet mass.
Massive enlargement of the spleen (splenomegaly) can result in a pooling of 80–90% of the platelets, producing peripheral blood thrombocytopenia. Removal of the spleen results in a transient thrombocytosis with a return to normal platelet concentrations in about 10 days.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 24 Hypersplenism
In a number of conditions, the spleen can become enlarged and, through exaggeration of its normal activities of filtering and phagocytosing, cause anemia, leukopenia, thrombocytopenia, or combinations of cytopenias. A diagnosis of hypersplenism is made when three conditions are met: (1) the presence of anemia, leukopenia, or thrombocytopenia in the peripheral blood, (2) the existence of a cellular or hyperplastic bone marrow corresponding to the peripheral blood cytopenias, and (3) the occurrence of splenomegaly. The correction of cytopenias following splenectomy confirms the diagnosis.
Hypersplenism has been categorized into two types: primary and secondary. Primary hypersplenism is said to occur when no underlying disease can be identified. The spleen functions abnormally and causes the cytopenia(s). This type of hypersplenism is very rare. Secondary hypersplenism occurs in those cases in which an underlying disorder causes the splenic abnormalities. Secondary hypersplenism has many and varied causes. Hypersplenism can occur secondary to compensatory (or workload) hypertrophy of this organ. Inflammatory and infectious diseases are thought to cause splenomegaly by an increase in the spleen’s immune defense functions. For example, an increase in clearing particulate matter can lead to an increase in number of macrophages, and hyperplasia of lymphoid cells can result from prolonged infection.
Several blood disorders can cause splenomegaly. In these disorders, intrinsically abnormal blood cells or cells coated with antibody are removed from circulation in large numbers (i.e., hereditary spherocytosis, immune thrombocytopenic purpura). Infiltration of the spleen with additional cells or metabolic by-products can also cause hypersplenism. Such conditions
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 25 include disorders in which the macrophages accumulate large quantities of undigestible substances; some of these disorders, such as Gaucher’s disease, will be discussed later. Neoplasms in which the malignant cells occupy much of the splenic volume can cause splenomegaly. If the tumor cells incapacitate the spleen, the peripheral blood will show evidence of hyposplenism (similar to the findings after splenectomy). Congestive splenomegaly can occur following liver cirrhosis with portal hypertension or congestive heart failure when blood that does not flow easily through the liver is rerouted through the spleen.
Splenectomy
Splenectomy can relieve the effects of hypersplenism; however, this procedure is not always advisable, especially when the spleen is performing a constructive role such as producing antibody or filtering protozoa or bacteria. Splenectomy appears to be most beneficial in patients with hereditary or acquired conditions in which erythrocytes or platelets are undergoing increased destruction, such as hemolytic disorders or immune thrombocytopenia. The blood cells are still abnormal after splenectomy, but the major site of their destruction is removed. Consequently, the cells have a more normal life span.
Splenectomy results in characteristic erythrocyte abnormalities that experienced clinical laboratory professionals can note easily on blood smears. After splenectomy, the erythrocytes often contain inclusions (i.e., Howell Jolly bodies, Pappenheimer bodies), and abnormal shapes can be seen. The lifespan of healthy erythrocytes is not increased after splenectomy. Other organs, primarily the liver, assume the culling function. Blood flow through the liver also is slowed by passage through sinusoids, which are lined with specialized macrophages called Kupffer cells. These
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 26 macrophages can perform functions similar to those of phagocytes in the splenic cords and marginal zone.
Even when a spleen is present, the liver, because of its larger blood flow, is responsible for removing most of the particulate matter of the blood. The liver, however, is not as effective as the spleen in filtering abnormal erythrocytes, probably because of the relatively rapid flow of blood past hepatic macrophages.
Acquired hyposplenism is a complication of sickle cell anemia. The spleen’s acidic, hypoxic, hypoglycemic environment leads to sickling of the erythrocytes in the spleen. This leads to blockage of the blood vessels and infarcts of the surrounding tissue. The tissue damage is progressive and leads to functional splenectomy (also referred to as autosplenectomy).
Common Blood Disorders
This section covers the common medication induced blood disorders that can impact an individual’s state of health. Blood disorders can involve disease of a number of body vessels, glands and organs, such the red or white blood cells and components of the blood, bone marrow, spleen and the lymph system. General guidance for health professionals to recognize signs and symptoms of an acute or chronic blood condition is offered here for appropriate diagnosis and treatment, and to help establish a framework for prevention and promotion of blood safety and health (discussed in more depth during the second part of this study series focused on Medication Induced Blood Discrasias: Diagnosis, Treatment And Prevention).
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 27 Aplastic Anemia
The term aplastic anemia is used to describe the condition of pancytopenia that is associated with a hypocellular bone marrow. The mature blood cells that are produced in aplastic anemia (AA) usually appear normal. Aplasia of the bone marrow is only one of several possible causes of peripheral blood pancytopenia, but pancytopenia due to causes other than AA can result in morphologically abnormal blood or bone marrow cells. Whereas AA is usually characterized by pancytopenia, granulocyte, platelet, and erythrocyte, levels may not be depressed uniformly.6
Aplastic anemia is a bone marrow failure disorder (or group of disorders) characterized by cellular depletion and fatty replacement of the bone marrow. The concomitant decreases in hematopoietic progenitors lead to diminished production of erythrocytes, leukocytes, and platelets and development of peripheral blood cytopenias or pancytopenia. The loss of functional bone marrow may occur following a variety of bone marrow insults that include drugs, chemicals, irradiation, infections, and immune dysfunction. Though the inciting mechanisms vary, all lead to the loss of bone marrow precursor cells or damage of the bone marrow microenvironment required to sustain bone marrow cell growth and differentiation. Thus, the hematopoietic progenitor cells that give rise to the various peripheral blood elements lose their ability to self renew and produce progeny. This leads to a loss of bone marrow cellular mass and bone marrow failure.
Clinical criteria that have been used to define aplastic anemia include (1) marrow of less than 25% normal cellularity and (2) at least two blood cytopenias defined as neutrophil count less than 500 per microliter or platelets less than 20,000 per microliter or anemia with corrected
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 28 reticulocyte count of less than 1%.6 With disease progression, concentrations of cells in all three cell lineages eventually become further depleted. This reflects an impaired proliferative capacity of the marrow stem cells, which lose their ability for normal cellular renewal.7
Aplastic anemia can be classified as either acquired or inherited. Historically, much attention has focused on an association between acquired AA and environmental exposures. Drugs, chemicals, radiation, infectious agents, and other factors have been linked to the development of acquired AA, which can be temporary or persistent. In most cases, no environmental link can be identified, and the cause is said to be idiopathic. The immune pathophysiologic model (discussed in the previous section) provides a unifying basis for understanding the disorder regardless of the presence or absence of environmental factors. Although acquired AA is more common in adults, it is also an infrequent cause of aplasia in children.
Drugs Associated with Aplastic Anemia
A wide variety of drugs have been associated with development of aplastic anemia. These are often the result of a nonpredictable or idiosyncratic reaction to a drug. As discussed previously, this may be a result of direct toxicity or development of an abnormal immune reaction whereby antibodies against a drug cross-react with bone marrow cells. The antibiotic chloramphenicol and the anti-inflammatory drug phenylbutazone are probably the best-documented examples of drugs causing aplastic anemia. The toxicity associated with these drugs is usually not related to the total dosage of the drug received, and drug-induced antibodies have been identified in only a few patients. Thus, the association between the drug and development of aplastic anemia is dependent on epidemiologic data and a
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 29 temporal relationship to drug ingestion and development of bone marrow failure.
The mechanism of drug-induced bone marrow failure suppression is usually unknown, and it is impossible to identify which patients will react adversely to a drug. Luckily, such idiosyncratic reactions to drugs are relatively rare. It is estimated that 1 person in 20,000 to 30,000 may have an idiosyncratic reaction to chloramphenicol, which is about 10 times the incidence of developing aplastic anemia for the general population not taking chloramphenicol.
Agents Regularly Producing Aplastic Anemia
Agents that regularly produce bone marrow hypoplasia with sufficient doses are discussed in this section and include:6,8,9 Ionizing radiation Benzene and benzene derivatives Chemotherapeutic agents (i.e., busulfan, vincristine) Drugs that produce bone marrow hypoplasia in an idiosyncratic manner
Type of Drug Relatively Frequent Rare Antimicrobials Chloramphenicol Penicillin, Streptomycin tetracycline Amphotericin B Sulfonamides Anticonvulsants Methylphenylethylhydantoin Methylphenylhydantoin Trimethadione Diphenylhydantoin Primidone Analgesics Phenylbutazone Aspirin Tapazole Hypoglycemic Tolbutamide Chlorpropamide agents Insecticides Chlorophenothane Parathion Miscellaneous Colchicine Acetazolamide Hair dyes
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 30 Chloramphenicol has been shown to cause two types of bone marrow effects. The most common reaction is a reversible bone marrow suppression that occurs while the patient is receiving the drug and is associated with vacuolization of bone marrow precursor cells and increased serum iron levels, reflecting ineffective erythropoiesis. The second reaction seen is development of an irreversible aplastic anemia that occurs weeks to months after drug exposure. This more severe reaction is not predictable on the basis of the dose, duration, or route of administration of the drug. Because of the strong association with development of aplastic anemia, chloramphenicol use has decreased. Currently the drug is administered only for specific indications when no other reasonable alternative exists.
A wide variety of other drugs have been implicated as direct suppressors of hematopoiesis and are occasionally associated with development of bone marrow aplasia. The incidence and predictability of bone marrow suppression vary with the type of drug. For example, chemotherapeutic agents are well known to regularly cause bone marrow hypoplasia in a dose-related manner. Other drugs (antibiotics, anticonvulsants, analgesics) are much less predictable. Knowledge of potential bone marrow side effects must be kept in mind when using these drugs and appropriate monitoring of peripheral blood indices performed. Often, drug-induced bone marrow hypoplasia is fully reversible on removal of the drug. A small minority of patients may develop irreversible damage.
Recent research has shown that exposure to drugs or chemical agents is not as commonly associated with aplastic anemia, although historically these associations were given prominent attention. A study conducted in Thailand, where the incidence of AA is 2–3 times higher than in the United States, indicated that an elevated risk of developing AA was associated with
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 31 exposure to only a small number of substances, including sulfonamides, thiazide diuretics, and mebendazole.
In the Thai study, an increased risk was not found for chloramphenicol, a drug frequently implicated in case reports of AA. Other drugs that have been implicated include gold, anticonvulsants, nonsteroidal analgesics, antiprotozoals, and antithyroid medications. Most individuals taking such medications, however, do not develop AA. One possible explanation is that persons with diminished P-glycoprotein, an efflux pump that is the product of the multi-drug resistance gene MDR-1, may have excessive accumulation of drugs that can increase susceptibility to HSC damage. In cases associated with drug exposure, the pathophysiology is thought to involve an abnormal immune response to the HSC. The following table provides a thorough overview of the most common drugs associated with aplastic anemia.
Chloramphenicol Chloramphenicol was one of the first drugs associated with aplastic anemia. A relatively common dose-dependent reversible bone marrow depression can appear in the second week of treatment, characterized by an inhibition of erythroid cells and anemia; this reaction is usually reversible by drug withdrawal. A more serious idiosyncratic aplastic anemia can evolve after more sustained usage.
Although less common, with wide variations in genetic susceptibility, this is a potentially fatal reaction. For this reason, chloramphenicol is now reserved for life threatening conditions and then only with regular monitoring. The evidence that ocular chloramphenicol is associated with aplastic anemia is extremely limited, and it remains the agent of choice for superficial eye infections.
NSAIDs NSAIDs have also been associated with aplastic anemia and agranulocytosis. Phenylbutazone, a pyrazole derivative, was
withdrawn because of aplastic anemia, which was fatal in 50 % of cases. Indomethacin, piroxicam, diclofenac and sulindac are also associated with aplastic anemia. Other NSAIDs have been linked, but on a more anecdotal basis.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 32 Disease- Aplastic anemia has also been associated with DMARDs, such as gold, sulfasalazine, penicillamine and leflunomide. Some have modifying recommendations for routine blood monitoring – falling platelet antirheumatic and neutrophil counts can indicate oncoming aplastic anemia. The Medicines and Healthcare products Regulatory Agency (MHRA) has drugs (DMARDs) received a number of reports of blood disorders associated with methotrexate, including aplastic anemia. It should be noted that error can contribute to blood disorders caused by methotrexate due to prescribing and dispensing errors, in particular the use of a daily instead of a weekly dose.
The National Patient Safety Agency (NPSA) has produced guidance to address this issue, and patient education is an important method of avoiding these potentially fatal errors.
Antiepileptic The use of antiepileptic drugs also appears to be linked to an increased risk of aplastic anemia. In a retrospective case-control drugs study, the risk of aplastic anemia had an odds ratio of 9.5 (95% CI 3.0-39.7) compared with no use. Use of multiple antiepileptic agents was more strongly associated with aplastic anemia, with carbamazepine and valproic acid particularly strongly associated.
Clinical Findings in AA
The onset of symptoms in AA is usually insidious and related to the cytopenias. Common initial signs are bleeding accompanied by petechial and mucosal hemorrhages and infection. Pallor, fatigue, and cardiopulmonary complications can be present as the anemia progresses.
Hepatosplenomegaly and lymphadenopathy are absent. Splenomegaly has occasionally been noted in later stages of the disease, but if found in the early stages, the diagnosis of aplastic anemia should be questioned.
Laboratory Findings6,9-11
Laboratory studies of peripheral blood and bone marrow are essential if a diagnosis of aplastic anemia is suspected.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 33 Peripheral Blood:
Pancytopenia is typical. Although the degree of severity can vary, the diagnosis of AA should be questioned unless the leukocyte count, erythrocyte count, and platelet count are all below the reference intervals. Hemoglobin is usually <70 g/L. Erythrocytes appear normocytic and normochromic, or they can be slightly macrocytic. The presence of nucleated erythrocytes and teardrops is not typical of AA but suggests marrow replacement (myelophthisic anemia).
Myelodysplastic syndrome, rather than AA, is suggested by the presence of dysplastic neutrophils and other abnormal cells. The relative reticulocyte count (%) can be misleading due to the severe anemia. Therefore, the reticulocyte count should always be determined in absolute concentration and/or be corrected for anemia before interpretation. The absolute reticulocyte count is usually <25×109/L. The corrected reticulocyte count is <1%. Most often, thrombocytopenia is present at the time of diagnosis. Neutropenia precedes leukopenia; initially, lymphocyte and monocyte counts are normal. Because of the neutropenia, the differential count reflects a relative lymphocytosis.
When the leukocyte count is below 1.5×109/L, an absolute lymphocytopenia is also present. The band to segmented neutrophil ratio is increased, and occasionally more immature forms are found. Neutrophil granules are frequently larger than normal and stain a dark red; these granules should be distinguished from toxic granules, which are bluish black. Flow cytometry of the peripheral blood can be ordered to detect CD59+ cells when PNH is suspected.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 34 Other abnormal findings are not specific for aplastic anemia but are frequently found associated with the disease. Hemoglobin F can be increased, especially in children. Erythropoietin is often increased, particularly when compared with the erythropoietin levels in patients with similar degrees of anemia. Serum iron is increased with >50% saturation of transferrin, reflecting erythroid hypoplasia. The clearance rate of iron (Fe59) from the plasma is decreased because of the decrease in iron utilization by a hypoactive marrow. Patients who are younger than age 50 should be screened for FA using tests for chromosomal breakage. Results of these tests will be normal in other forms of inherited AA and in acquired/idiopathic forms of AA.
Bone Marrow:
Examination of the bone marrow is necessary to differentiate aplastic anemia from other diseases accompanied by pancytopenia. In AA, the bone marrow is hypocellular with >70% fat. Thus, it is often difficult to obtain an adequate sample. Bone marrow infiltration with granulomas or cancer cells can lead to fibrosis, also resulting in a hypocellular dry tap on aspiration.
Both aspiration and biopsy are needed for a correct diagnosis. It is recommended that several different sites be aspirated because focal sampling of the marrow can be misleading. Some areas of acellular stroma and fat can be infiltrated with clusters of lymphocytes, plasma cells, and reticulum cells. Areas of residual hematopoietic tissue termed hot spots can be found primarily early in the disease but can occasionally be found in severe refractory cases. Iron staining reveals many iron granules in macrophages, but granules are rarely seen in normoblasts. Flow cytometry should be performed; the percentage of CD34+ cells in the bone marrow in
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 35 AA is typically <0.3%. Bone marrow karyotyping is useful for differentiating hypocellular forms of myelodysplastic syndromes from aplastic anemia.
Prognosis and Therapy6,11
Recent advances in treatment have tempered the previously grim prognosis of patients diagnosed with aplastic anemia. HSCT and immunosuppressive therapy (IST) have greatly improved survival. Presently, the 5-year survival rate is 79%.
Choice of definitive therapy for severe acquired AA depends on the age of the patient and availability of a matched donor. HSCT is recommended for patients up to age 45 who have a matched sibling donor, although some recommendations extend the age limit to age 55. HSCT is also recommended for patients up to age 21 with a fully compatible HLA-matched unrelated donor. IST is recommended for patients without a matched related donor, the situation faced by the majority of patients with aplastic anemia. Before beginning HSCT or IST, putative causative drugs should be withdrawn or the patient removed from a hazardous environment. The immediate treatment is often supportive with the administration of erythrocytes, platelets, and antibiotics. Granulocyte transfusions can be given to severely neutropenic patients with life-threatening sepsis. To avoid alloimmunization, transfusion should be minimized if HSCT is anticipated. Irradiated and/or leukocyte-reduced blood products can be ordered. Hematopoietic growth factors such as G-CSF generally do not have a beneficial effect on patients with AA and may increase the risk of MDS.
HSCT using cells collected from bone marrow has become a relatively common procedure and is curative in many patients with aplastic anemia. Bone marrow is preferred over peripheral blood stem cells due to the
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 36 increased risk of graft-vs-host disease with the latter. Antithymocyte globulin (ATG) and cyclosporine are typically used as preconditioning regimens to suppress the immune response of the recipient. Preconditioning is nonmyeloablative.
The current 5-year survival rate is 77% for HLA-matched sibling donors. Survival rates are highest for children and for patients who have been minimally transfused. Treatment complications and post-transplant mortality remain high, especially in older patients; therefore, the probability for long- term cure must be weighed against the inherent risks of complications, including graft-vs-host disease and early and late toxicities of the conditioning regimen. Although engraftment of HSCs is successful in many cases, some transplants, even when performed between identical twins, do not correct the AA. These unsuccessful transplants suggest that the donor HSC growth is suppressed by the same immune mechanism that induced the original aplasia. An additional constraint to HSCT is that matched sibling donors are available for only 20–30% of patients with aplastic anemia.
Combined, intensive immunosuppressive therapy (IST) using ATG in combination with cyclosporine has become standard treatment for those patients with acquired severe aplastic anemia who lack a suitable bone marrow donor. IST is effective in restoring hematopoiesis in 60–90% of patients who are over 45 or who lack an HLA-matched sibling donor. More favorable outcomes are observed in children. Relapse requiring additional IST occurs in 30–40% of patients. About 15% of patients treated with IST develop clonal disorders such as paroxysmal nocturnal hemoglobinuria (PNH), leukemia, and myelodysplastic syndromes.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 37 Neutropenia/Agranulocytosis12-21
Neutropenia is defined as an absolute decrease in the number of circulating neutrophils and is suspected when patients present with absolute neutrophil counts of less than 1.5 × 109/L. The absolute neutrophil count (ANC) can be obtained by multiplying the total WBC count by the percentage of neutrophils (and bands) seen in the differential cell count.
A low neutrophil count is not the sole indicator of disease and should be correlated with patient history as well as clinical and laboratory findings. The normal level of circulating neutrophils varies with age and race, and refers to mature polymorphonuclear and band forms only. Recurrent bacterial infections are the hallmark of persistent neutropenia, with the clinical severity being reflected by the absolute neutrophil count as well as the frequency and duration of neutropenic episodes.
Neutropenia can range from mild, with absolute counts from 1.0 to 1.5 × 109/L, to moderate, with counts from 0.5 to 1.0 × 109/L, to severe, with counts less than 0.5 × 109/L. Life-threatening infections are not generally observed until blood counts fall below 0.2 × 109/L. Most of the neutrophils are contained in the bone marrow, either as mitotically active (one third) or postmitotic mature cells (two thirds). Granulocytopenia is defined as a reduced number of blood granulocytes, namely neutrophils, eosinophils, and basophils. However, the term granulocytopenia is often used synonymously with neutropenia and, in that sense, is again confined to the neutrophil lineage alone.
Neutropenia is defined in terms of the absolute neutrophil count. The ANC is calculated by multiplying the total white blood cell (WBC) count by the percentage of neutrophils (segmented neutrophils or granulocytes) plus the nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 38 band forms of neutrophils in the complete blood count (CBC) differential. It should be noted that many modern automated instruments actually calculate and provide the ANC number in their reports. These instruments do not separately analyze bands from segmented neutrophils, and so the combined number is termed the absolute neutrophil count (ANC), representing both bands and more mature segmented neutrophils. If a band number is reported separately, usually by smear review, then one can divide the ANC into bands and segmented neutrophils by subtracting the absolute band number from the total ANC. The lower limit of the reference value for ANC in adults varies in different laboratories from 1.5-1.8 109/L or 1500-1800/µL (mm3). For practical purposes, a value lower than 1500 cells/µL is generally used to define neutropenia. Age, race, genetic background, environment, and other factors can influence the neutrophil count. For example, black people may have a lower but normal ANC value of 1000 cells/µL, with a normal total WBC count.
Neutropenia is classified as mild, moderate, or severe, based on the ANC. Mild neutropenia is present when the ANC is 1000-1500 cells/µL, moderate neutropenia is present with an ANC of 500-1000/µL, and severe neutropenia refers to an ANC lower than 500 cells/µL. The risk of bacterial infection is related to both the severity and duration of the neutropenia.
The term agranulocytosis is used to describe a more severe subset of neutropenia. Agranulocytosis refers to a virtual absence of neutrophils in peripheral blood. It is usually applied to cases in which the ANC is lower than 100/μL. The reduced number of neutrophils makes patients extremely vulnerable to infection. Cardinal symptoms include fever, sepsis, and other manifestations of infection.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 39 Acquired agranulocytosis is a rare blood disorder that affects males and females in equal numbers. People who are taking certain medications such as cancer (chemotherapeutic) drugs, alkylating agents, anti-thyroid drugs, dibenzepin compounds, or other drugs can be at risk for this disorder. Causes other than drugs can include chemicals, infective agents, ionizing radiation, immune mechanisms, primary bone marrow failure syndromes, and heritable genetic aberrations. Some cases, such as those from benign familial neutropenia, are characterized by only mild neutropenia and are of no obvious significance for health. This article is limited to discussing neutropenia (ANC <1500/µL) and agranulocytosis (ANC <100/µL). It does not address the transient neutropenia associated with cancer chemotherapy, nor does it consider agranulocytosis occurring as part of primary marrow- failure syndromes (i.e., aplastic anemia, pancytopenia, acute leukemia, myelodysplastic syndromes).
Acquired agranulocytosis, as previously mentioned, is a rare, drug-induced blood disorder, and it is characterized by a severe reduction in the number of white blood cells (granulocytes) in the circulating blood. The name granulocyte refers to grain-like bodies within the cell. Granulocytes include basophils, eosinophils, and neutrophils. Although acquired agranulocytosis may be caused by a variety of drugs, certain drugs are more commonly administered with standard monitoring precautions for possible drug-induced agranulocytosis, such as with chemotherapeutic agents as well as specific antipsychotic medications, for example, clozapine.
The symptoms of acquired agranulocytosis come about as the result of interference in the production of granulocytes in the bone marrow. People with this disorder are susceptible to a variety of bacterial infections, usually caused by otherwise benign bacteria found in the body. Not
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 40 infrequently, painful ulcers also develop in mucous membranes that line the mouth and/or the gastrointestinal tract.
Signs and Symptoms
The first symptoms of acquired agranulocytosis are usually those associated with a bacterial infection such as general weakness, chills, fever, and/or extreme exhaustion. Symptoms that are associated with rapidly falling white blood cell levels (granulocytopenia) may include the development of infected ulcers in the mucous membranes that line the mouth, throat, and/or intestinal tract. Some people with these ulcers may experience difficulty swallowing due to irritation and pain.
Granulocytopenia causes a concurrent decrease in the number of neutrophils in the circulating blood (neutropenia). As neutrophil levels decrease the susceptibility of patients with acquired agranulocytosis to bacterial infections becomes even greater. Fevers and abnormal enlargement of the spleen (splenomegaly) are characteristic features of neutropenia. If neutropenia is not treated, bacterial infections can lead to life-threatening complications such as bacterial shock or bacterial contamination of the blood (sepsis). Chronic acquired agranulocytosis generally progresses more slowly than acquired agranulocytosis. Canker sores in the mouth and chronic inflammation of the gums (gingivitis) may be recurring symptoms. Other systemic infections may recur regularly.
Causes
Acquired agranulocytosis is almost invariably caused by exposure to drugs and/or chemicals. Any chemical or drug that depresses the activity of the bone marrow may cause agranulocytosis. Some drugs cause this reaction in
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 41 anyone given large enough doses. Other drugs may cause an idiosyncratic reaction in one person but not in another. Clinicians do not understand why some people are susceptible to agranulocytosis and others are not.
In some instances, the action of some drugs or chemicals suggests that the immune system is involved. In the case of gold, or anti-thyroid drugs, or quinidine, among others, antibodies are created that appear to break the granulocytes down. Other drugs that interfere with, or inhibit, granulocyte colony formation may induce agranulocytosis. Drugs with this characteristic include valproic acid, carbamazepine, and the beta-lactam antibiotics.
As mentioned, a complicating factor is that several commonly used anti- cancer drugs are prone to cause agranulocytosis, thus interfering with treatment. This also may be said for several antipsychotic and mood stabilizing medications. A variety of drugs can cause acquired agranulocytosis and neutropenia by destroying special cells in the bone marrow that later mature and become granulocytes (precursors), such as phenytoin, pyrimethamine, methotrexate, and cytarabine. In rare cases of acute acquired agranulocytosis, certain drugs may induce destructive action of certain white blood cell antibodies (leukocyte isoantibodies), such as phenylbutazone, gold salts, sulfapyridine, aminopyrine, meralluride, and dipyrine. The antithyroid drugs carbimazole and propylthiouracil carry a relatively high risk of hematological dysfunctions including agranulocytosis.
Females and those over 65 years of age may have an increased risk. Although some have argued for routine blood monitoring, the balance of opinion is that monitoring is not considered worthwhile due to the rapid onset of the adverse effect that monitoring would not capture. Recurrence of agranulocytosis has also been reported when switching from one drug to
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 42 another, such as with carbimazole to propylthiouracil. Approximately half the fatalities caused by carbimazole and propylthiouracil reportedly resulted from agranulocytosis and neutropenia. Patients taking anti-thyroid drugs should be told to notify their medical provider at once if they experience fever, a sore throat, mouth ulcers, bruising, malaise or nonspecific illness. Such reports should be treated as medical emergencies.
The atypical antipsychotic medication clozapine is a known cause of agranulocytosis. It is associated with a 2-3 per cent incidence of neutropenia and a case fatality rate of between 4 and 16 per cent. For this reason, its use is restricted to patients enrolled in strict blood-monitoring programs, although it has been argued that the risk of agranulocytosis after six months is sufficiently reduced to challenge the continued necessity for such strict monitoring. Other psychotropic drugs and antidepressants have been associated with agranulocytosis. Chlorpromazine is associated with a delayed-onset agranulocytosis, with severe cases occurring in 0.1 per cent of patients taking standard doses. Antibiotic agents have also been associated with agranulocytosis including co-trimoxazole, which has a variety of serious hematological effects.
Diagnosis
The diagnosis of acquired agranulocytosis is made by combining a thorough history with tests to confirm abnormally low levels of granulocytes in the circulating blood. Regular periodic blood testing is required for individuals who take drugs that place them at high risk for acquired agranulocytosis. In some cases (i.e., people who are taking clozapine), blood tests to monitor granulocyte levels are done on a weekly basis.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 43 Treatment
Filgrastim has been designated an orphan drug (developed to treat a rare medical condition) and approved by the U.S. Food and Drug Administration (FDA) for the treatment of severe, chronic neutropenia; and it has become a standard treatment for acquired agranulocytosis. Filgrastim is one of a class of colony-stimulating factors that does, indeed, stimulate the proliferation and differentiation of neutrophils. Amgen, Inc., uses recombinant DNA technology, and manufactures it.
The treatment of acquired agranulocytosis includes the identification and elimination of drugs or other agents that induce this disorder. Antibiotic medications may also be prescribed if there is a positive blood culture for the presence of bacteria or if a significant local infection develops. Treatment in adults with antibiotics should be limited to about 7-10 days since longer duration carries with it a greater risk of kidney (renal) complications and may set the stage for a new infection. When granulocyte levels return to a near normal range, fever and infections will generally subside.
There is no definitive therapy that can stimulate bone marrow (myeloid) recovery. Corticosteroids are sometimes used to treat shock induced by overwhelming bacterial infection. However, these drugs are not recommended for the treatment of acute agranulocytopenia because they may mask other bacterial infections.
People with abnormally low levels of immune factors in their blood (hypogammaglobulinemia) associated with acquired agranulocytosis are usually treated with infusions of gamma globulin. Mouth and throat ulcers associated with acquired agranulocytosis can be soothed with gargles of salt (saline) or hydrogen peroxide solutions. Anesthetic lozenges may also help
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 44 to relieve irritation in the mouth and throat. Mouthwashes that contain the antifungal drug nystatin can be used to treat oral fungal infection (i.e., thrush or candida). A semi-solid or liquid diet may become necessary during episodes of acute oral and gastrointestinal inflammation.
People with chronic granulocytopenia associated with acquired agranulocytosis need to be hospitalized during acute episodes of infection. These affected individuals should be taught to recognize the early symptoms and signs of acute infection and to seek immediate medical attention when necessary. The therapy for chronically affected individuals is similar to that for the acute form of the disease. People with chronic granulocytopenia, who take low-dose oral antibiotics on a rotating basis, must also be monitored for the infections caused by drug-resistant bacteria as well as infections with opportunistic organisms (i.e., fungi, cytomegalovirus).
Investigational Therapies
Acquired agranulocytosis may be helped through the use of new biotechnology drugs including granulocyte-colony stimulating factor (G-CSF) and granulocyte macrophage-CSF (GM-CSF). G-CSF and GM-CSF may stimulate the production and development of immature blood cells that later become granulocytes, ultimately increasing the number of granulocytes in the blood. These treatments are currently under investigation, and more studies are needed to determine the long-term safety and effectiveness of these factors for the treatment of acquired agranulocytosis.
Megaloblastic Anemia22-28
Megaloblastic anemia is classified as a nuclear maturation defect. Anemia is attributed primarily to a large degree of ineffective erythropoiesis resulting
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 45 from disrupted DNA synthesis. The anemia was called megaloblastic in an attempt to describe the giant, abnormal-appearing erythroid precursors (megaloblasts) in the bone marrow. The generic word megaloblast describes any maturation stage of the megaloblastic erythroid series (i.e., polychromatic megaloblast). Other nucleated cells of the marrow are also typically abnormal.
About 95% of megaloblastic anemias are caused by deficiencies of vitamin B12 (cobalamin) or folic acid, which are vitamins necessary as coenzymes for nucleic acid synthesis. In the majority of cases, cobalamin deficiency is secondary to a deficiency of intrinsic factor (IF), a protein necessary for absorption of cobalamin, rather than to a nutritional deficiency of the vitamin. Folic acid deficiency, on the other hand, is most often due to an inadequate dietary intake. Inherited disorders affecting DNA synthesis or vitamin metabolism are rare causes of megaloblastosis.
The onset of megaloblastic anemia is usually insidious; because the anemia develops slowly, it produces few symptoms until the hemoglobin and hematocrit are significantly depressed. Patients can present with typical anemic symptoms of lethargy, weakness, and a yellow or waxy pallor. Dyspeptic symptoms are common. Glossitis with a beefy red tongue, or more commonly a smooth pale tongue, is characteristic. Loss of weight and loss of appetite are common complaints. In pernicious anemia, atrophy of the gastric parietal cells causes decreased secretion of intrinsic factor and hydrochloric acid. Bouts of diarrhea can result from epithelial changes in the gastrointestinal tract.
Neurological disturbances occur only in cobalamin deficiency, not in folic acid deficiency. They are the most serious and dangerous clinical signs because
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 46 neurological damage can be permanent if the deficiency is not treated promptly. The patient’s initial complaints occasionally are related to neurological dysfunction rather than to anemia. Neurological damage has been reported to occur even before anemia or macrocytosis in some cases, particularly in elderly people. The bone marrow, however, usually reveals megaloblastic changes even in the absence of anemia. Tingling, numbness, and weakness of the extremities reflect peripheral neuropathy. Loss of vibratory and position (proprioceptive) sensations in the lower extremities can cause the patient to have an abnormal gait. The patient’s relatives sometimes note mental disturbances such as loss of memory, depression, and irritability.
Megaloblastic madness is a term used to describe severe psychotic manifestations of cobalamin deficiency. A patient with severe anemia occasionally is asymptomatic, which is probably a reflection of a very slowly developing anemia. It has been suggested that cobalamin deficiency should be suspected in all patients who have an unexplained anemia and/or neurological disturbances or in individuals who are at risk of developing a deficiency such as elderly people or those with intestinal diseases.
A large number of drugs that act as metabolic inhibitors can cause megaloblastosis. Some of these drugs are used in chemotherapy for malignancy. Although aimed at eliminating rapidly proliferating malignant cells, these drugs are not selective. Any normal proliferating cells, including hematopoietic cells, are also affected. Megaloblastic anemia has also been associated with other drugs including oral contraceptives, long-term anticoagulant drugs, phenobarbital, primidone, and phenytoin. Anemia occasionally is not present even though serum and erythrocyte folate are depressed.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 47 DNA Base Inhibitors
Pyrimidine Purine Antimetabolites Other
Azauridine Acyclovir Cytosine arabinoside Azacytidine Adenosine Fluorocytidine Cyclophosphamide arabinoside Fluorouracil Zidovudine (AZT) Azathioprine Hydroxyurea Gancyclovir Methotrexate Mercaptopurine Thioguanine Vidarabine
Laboratory Findings
Laboratory tests are critical to a diagnosis of megaloblastic anemia. The routine CBC with a review of the blood smear gives important diagnostic clues and helps in selecting reflex tests.
Megaloblastic anemia is typically a macrocytic, normochromic anemia. The MCV is usually >100 fL and can reach a volume of 140 fL. However, an increased MCV is not specific for megaloblastic anemia. The MCH is increased because of the large cell volume, but the MCHC is normal. In cobalamin deficiency, a macrocytosis can precede the development of anemia by months to years. On the other hand, the MCV can remain within the reference interval. Epithelial changes in the gastrointestinal tract can cause iron absorption to be impaired. If an iron deficiency (which characteristically produces a microcytic, hypochromic anemia) coexists with megaloblastic anemia, macrocytosis can be masked, and the MCV can be in the normal range. nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 48 Common Laboratory Values in Megaloblastic and Nonmegaloblastic Macrocytosis
Laboratory Value Megaloblastic Nonmegaloblastic Macrocytosis Macrocytosis
WBC count Decreased Normal
Platelet count Decreased Normal
RBC count Decreased Decreased
Hemoglobin Decreased Decreased
Hematocrit Decreased Decreased
MCV Usually >110 fL >100 fL
RBC morphology Ovalocytes, Howell-Jolly Polychromasia, target cells, and bodies, polychromasia stomatocytes (liver disease), schistocytes (hemolytic anemias)
Hypersegmentation Present Absent of neutrophils
Reticulocyte count Normal to decreased Normal, decreased, or increased
Serum cobalamin Decreased in cobalamin Usually normal deficiency
Serum folate Decreased in folate Normal (except is decreased in deficiency alcoholism)
FIGLU Increased in folate Normal deficiency
MMA Increased in B12 Normal deficiency
Homocysteine Increased Normal
Serum bilirubin Increased Normal to increased
LD Increased Normal to increased
MCV = mean corpuscular volume. FIGLU = formiminoglutamic acid. MMA = methylmalonicacid. LD = lactic dehydrogenase.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 49 Other conditions that have been shown to coexist with megaloblastic anemia in the absence of an increased MCV include thalassemia, chronic renal insufficiency, and chronic inflammation or infection. Sometimes these coexisting causes of anemia are not recognized until after the megaloblastic anemia has been treated. It has been suggested that if coexisting iron deficiency, thalassemia, or chronic disease is suspected, patient medical history, racial/ethnic background, and previous MCV should be considered.
Hematologic parameters vary considerably. The hemoglobin and erythrocyte count range from normal to very low. The erythrocyte count is occasionally <1×1012/L. However, anemia is not always evident. In one study of 100 patients with confirmed cobalamin deficiency, only 29% had a hemoglobin of <12g/dL. This is significant because neurologic symptoms can be present even if the MCV and/or hematocrit are normal. Because the abnormality is a nuclear maturation defect, the megaloblastic anemias affect all three blood cell lineages: erythrocytes, leukocytes, and platelets. This is unlike most other anemias that typically involve only erythrocytes.
The leukocyte count can be decreased due to an absolute neutropenia. Platelets can also be decreased but do not usually fall below 100×109/L . The relative reticulocyte count (percentage) is usually normal; however, because of the severe anemia, the corrected reticulocyte count is <2%, the absolute reticulocyte count is low, and RPI is <2.
The distinguishing features of megaloblastic anemia on the stained blood smear include the triad of oval macrocytes (macro-ovalocytes), Howell-Jolly bodies, and hypersegmented neutrophils. Anisocytosis is moderate to marked with normocytes and a few microcytes in addition to the macrocytes. Poikilocytosis can be striking and is usually more so when the anemia is
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 50 severe. Polychromatophilia and megaloblastic erythroblasts can be seen, especially when the anemia is severe, indicating the futile attempt of the bone marrow to increase peripheral erythrocyte mass. Cabot rings occasionally can be seen in erythrocytes. Granulocytes and platelets can also show changes evident of abnormal hematopoiesis.
Hypersegmented neutrophils can be found in megaloblastic anemia even in the absence of macrocytosis. Finding 5% or more neutrophils with five lobes or one neutrophil with six or more lobes is considered hypersegmentation. This finding of hypersegmented neutrophils is considered highly sensitive and specific for megaloblastic anemia. Therefore, hypersegmented neutrophils offer an important clue to megaloblastic anemia in the face of a coexisting disease that tends to keep erythrocyte volume <100 fL. One study showed that in patients with renal disease, iron deficiency, or chronic disease with a normal or decreased MCV and 1% hypersegmented
neutrophils, 94% had vitamin B12 or folic acid deficiency. If 5% hypersegmented neutrophils were counted, the incidence of the vitamin B12 or folic acid deficiency increased to 98%. Hypersegmented neutrophils tend to be larger than normal neutrophils. A mild shift to the left with large hypogranular bands can also be noted. Platelets can be large, especially when the platelet count is decreased.
If the CBC results suggest megaloblastic anemia, further testing is necessary to distinguish the cause. Although no major medical organization has published guidelines for reflex testing, the most common next step is to measure serum cobalamin and serum or red cell folate. Laboratories use different methods (chemiluminescence, radioassay) to measure cobalamin, so there is no “gold standard” to use as a reference interval. Generally values <150pg/mL are consistent with cobalamin deficiency, whereas levels
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 51 >400pg/mL suggest adequate cobalamin. Borderline levels (150–400 pg/mL) can be associated with cobalamin deficiency.
Measurement of erythrocyte folate is not influenced as much by recent dietary changes as is serum folate and gives an accurate estimate of the average folate levels over the preceding several months. On the other hand, if there is a cobalamin deficiency, folate will leak out of the cells, which will give a false low red cell folate and false increased serum folate. In addition, red cell folate is measured by folate-binding protein assays that rely on chemiluminescence methodology. These methods show considerable analytic variability. Therefore, the less expensive serum folate measurement is preferred for initial testing. If serum folate is >4 ng/mL, folate deficiency can be ruled out.
Early megaloblastic changes can be detected by testing for methylmalonic acid (MMA) and homocysteine levels in the blood. Tests for these metabolites are intermediates in folate and cobalamin metabolism and are elevated early in functional vitamin deficiencies. Tests for these metabolites are more sensitive than serum cobalamin levels and increase earlier than a drop in the cobalamin level. By performing tests for both MMA and homocysteine, it is possible to differentiate cobalamin deficiency from folate deficiency. Homocysteine is elevated in folate deficiency, whereas MMA is usually normal. On the other hand, both homocysteine and MMA are elevated in cobalamin deficiency.
An increase in both MMA and homocysteine is also found in combined cobalamin and folate deficiencies. In these cases, clinical information is important to help establish a differential diagnosis. A block in the metabolism of histidine to glutamic acid occurs in folic acid deficiency and
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 52 causes increased urinary excretion of formiminoglutamic acid (FIGLU), an intermediate metabolite, after the administration of histidine. These metabolites return to normal levels when the appropriate vitamin is given to the patient. It is recommended that clinicians first use the lower cost tests of serum cobalamin and serum folate to diagnose cobalamin and folate deficiencies and use the higher cost MMA and homocysteine tests if cobalamin and folate test results are not definitive.
The large degree of ineffective erythropoiesis results in hemolysis in the marrow and an increase in plasma iron turnover, serum iron, indirect bilirubin, and urobilinogen. The characteristic marked increase in fractions 1 and 2 of serum lactic dehydrogenase (LD) is partially caused by the destruction of megaloblasts rich in LD. The increase is roughly proportional to the degree of anemia. Haptoglobin, uric acid, and alkaline phosphatase are decreased.
Bone Marrow
If physical examination, patient history, and peripheral blood findings suggest megaloblastic anemia, a bone marrow examination can help establish a definitive diagnosis. In megaloblastic states, the bone marrow is hypercellular with megaloblastic erythroid precursors and a decreased M:E ratio. In a long-standing anemia, red marrow can expand into the long bones. About half the erythroid precursors typically show megaloblastic changes.
Megaloblasts are large nucleated erythroid precursors that display nuclear- cytoplasmic asynchrony with nuclear maturation lagging behind cytoplasmic maturation. The nucleus of the megaloblast contains loose, open chromatin that stains poorly; cytoplasmic development continues in a normal fashion. nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 53 At each stage of development, the cells contain more cytoplasm with a more mature appearance relative to the size and maturity of the nucleus (resulting in a decreased nuclear:cytoplasmic [N:C] ratio).
The megaloblastic features are more easily noted in later stages of erythroid development, especially at the polychromatophilic stage in which the presence of hemoglobin mixed with RNA gives the cytoplasm the gray-blue color typical of this erythroid precursor. The polychromatophilic megaloblast nucleus, however, still has an open (lacy) chromatin pattern more typical of an earlier stage of development.
Leukocytes and platelets also show typical features of a nuclear maturation defect as well as ineffective leukopoiesis and thrombopoiesis. Giant metamyelocytes and bands with loose, open chromatin in the nuclei are diagnostic. The myelocytes can show poor granulation as do more mature stages. Megakaryocytes can be decreased, normal, or increased. Maturation, however, is distinctly abnormal; larger than normal forms can be found with separation of nuclear lobes and nuclear fragments.
Therapy
Therapeutic trials in megaloblastic anemia using physiologic doses of either vitamin B12 or folic acid produce a reticulocyte response only if the specific vitamin that is deficient is being administered. For instance, small doses (1 mcg) of vitamin B12 given daily produce a reticulocyte response in cobalamin deficiency but not in folic acid deficiency. On the other hand, large therapeutic doses of cobalamin or folic acid can induce a partial response to the other vitamin deficiency as well as the specific deficiency.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 54 Generally, it is best to determine which deficiency exists and to treat the patient with the specific deficient vitamin. Large doses of folic acid will correct the anemia in cobalamin deficiency but do not correct or halt demyelination and neurologic disease. This makes diagnosis and specific therapy in cobalamin deficiency critical. Specific therapy causes a rise in the reticulocyte count after the fourth day of therapy. Reticulocytosis peaks at about 5–8 days and returns to normal after 2 weeks.
The degree of reticulocytosis is proportional to the severity of the anemia with more striking reticulocytosis in patients with severe anemia. The hemoglobin rises about 2–3 g/dL every 2 weeks until normal levels are reached. The marrow responds quickly to therapy, as evidenced by pronormoblasts (normal) appearing within 4–6 hours and nearly complete recovery of erythroid morphologic abnormalities within 2–4 days. Granulocyte abnormalities disappear more slowly. Hypersegmented neutrophils can usually be found for 12–14 days after therapy begins.
Specific therapy can reverse the peripheral neuropathy of cobalamin deficiency, but spinal cord damage is usually irreversible. Pernicious anemia must be treated with lifelong monthly parenteral doses of hydroxycobalamin (OHCbl) because of these patients’ inability to absorb oral cobalamin. Recently, it was reported that large doses of cobalamin therapy (usually 1000–2000 mcg/day) administered orally could be feasible if the patient is followed carefully. The oral treatment can be better tolerated and less expensive. The rationale behind oral therapy using large doses of vitamin is that a small amount (from 1 to 3%) of the vitamin is absorbed by diffusion without intrinsic factor.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 55 Hemolytic Anemia29-41
Drug-associated hemolytic anemia is thought to occur in approximately one in a million people, with four distinct mechanisms proposed for the majority of cases: immune complex formation, hapten formation, autoantibody production and, in those with glucose-6-phosphate dehydrogenase (G6PD) deficiency, oxidative red cell damage. Immune complexes seem to be the major cause, with quinine, quinidine, rifampicin, methotrexate, sulphonylureas and antihistamines among those associated. Penicillin has been associated with hapten formation – around 3 per cent of patients receiving high doses will develop a positive antiglobulin test, of which a small proportion will develop hemolytic anemia. A positive Coombs’ test can distinguish immune reactions from other causes of hemolytic anemia.
Hemolysis caused by G6PD deficiency is dose dependent and increases with cumulative doses. Drugs with a definite risk of hemolysis include nitrofurantoin, primaquine, quinolones and sulphonamides; and, prescribers are warned of G6PD deficiency and further information on drugs to be avoided. A hemolytic state exists when the in vivo survival of red cells is shortened. The presence of anemia in an individual patient is, however, dependent on the degree of hemolysis and the compensatory response of the erythroid elements of the bone marrow. Normal bone marrow is able to increase its output about six- to eightfold, so that anemia is not manifest until this capacity is exceeded, corresponding to a red cell life span of about 15 to 20 days or less. Anemia may, however, occur with more moderate shortening of the red cell life span if there is an associated depression of bone marrow function, which may occur with certain systemic diseases or exposure to chemicals or drugs.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 56 A useful classification of the hemolytic anemias entails their subdivision into those disorders associated with an intrinsic (intracorpuscular) defect of the red cell and those associated with an extrinsic (extracorpuscular) abnormality. Red cells from a patient with an intracorpuscular defect have a shortened survival in both the patient and a normal recipient, whereas normal donor red cells survive normally in the patient. In contrast, normal red cells are destroyed more rapidly when transfused into a patient with an extracorpuscular abnormality. The patient's red cells, when transfused into a healthy recipient, have normal survival, provided that they have not been irreversibly damaged. Hemolytic states have also traditionally been regarded as intravascular or extravascular; that is, sequestration occurs in reticuloendothelial tissue. However, vigorous extravascular hemolysis may often be associated with signs of hemoglobin release into the plasma such as hemoglobinemia and decreased haptoglobin levels. The distinction still is useful from a clinical standpoint because certain hemolytic states are associated with predominantly intravascular hemolysis (i.e., paroxysmal nocturnal hemoglobinuria and infections caused by Clostridium or Plasmodium falciparum).
Classification of Immune Hemolytic Anemias
Hemolytic anemias may be classified as follows:
Intracorpuscular defects Hereditary defects: Defects in the red cell membrane Enzyme defects Hemoglobinopathies Thalassemia syndromes Acquired defects Paroxysmal nocturnal hemoglobinuria nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 57 Extracorpuscular defects Immune hemolytic anemias Infections Exposure to chemicals and toxins Exposure to physical agents Microangiopathic and macroangiopathic hemolytic anemias Splenic sequestration (hypersplenism) General systemic disorders (in which hemolysis is not the dominant feature of the anemia)
Determining the underlying process of immune hemolysis is important because each type requires a specific treatment regimen. Initially, immune hemolytic anemia can be classified into three broad categories based on the stimulus for antibody production, which is listed below.
Classification Causes
Autoimmune Warm-reactive antibodies (37°C)
Primary or idiopathic
Secondary
Autoimmune disorders (systemic lupus erythematosus, rheumatoid arthritis, and others)
Chronic lymphocytic leukemia and other immunoproliferative diseases
Viral infections
Neoplastic disorders
Chronic inflammatory diseases
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 58 Classification Causes
Cold-reactive antibodies (<30°C)
Primary or idiopathic (cold hemagglutinin disease)
Secondary
Infectious diseases (Mycoplasma pneumonia, Epstein-Barr virus, other organisms)
Lymphoproliferative disorders
Paroxysmal cold hemoglobinuria
Idiopathic
Secondary
Viral syndromes
Syphilis (tertiary)
Mixed type
DAT negative
Drug induced Drug dependent
Drug independent
Nonimmunologic protein adsorption (NIPA)
Alloimmune Hemolytic transfusion reaction
Hemolytic disease of the fetus and newborn
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 59 Autoimmune hemolytic anemia (AIHA) is a complex and incompletely understood process characterized by an immune reaction against self- antigens and shortened erythrocyte survival. Individuals produce antibodies against their own erythrocyte antigens (autoantibodies), which are usually directed against high-incidence antigens (antigens present on the erythrocytes of most people). The autoantibodies characteristically react not only with the individual’s own erythrocytes but also with the erythrocytes of other individuals carrying that antigen. The reactions that occur with autoantibodies include sensitization (attachment of antibody or complement to the erythrocytes), agglutination of the erythrocytes, or erythrocyte lysis.
Autoimmune hemolytic anemias are further classified as warm or cold hemolytic anemia based on clinical symptoms and on the optimal temperature at which the antibody reacts in vivo and in vitro. Some antibodies react best at body temperature (37°C); the anemia they produce is termed warm autoimmune hemolytic anemia (WAIHA). About 70% of the AIHAs are of the warm type. The majority of warm autoantibodies are of the IgG class (most frequently IgG1) and cause extravascular hemolysis of the erythrocyte. A few warm-reacting autoantibodies of either the IgM or IgA class have been identified.
Cold hemolytic anemias, on the other hand, are usually due to the presence of an IgM antibody with an optimal thermal reactivity below 30°C. Hemolysis with cold-reacting antibodies results from IgM binding to and activating complement. The IgM antibody attaches to erythrocytes in the cold and fixes complement. After warming, the antibody dissociates from the cell, but the complement remains, either causing direct cell lysis or initiating extravascular destruction. Included in the cold hemolytic anemia classification is a special condition, paroxysmal cold hemoglobinuria (PCH),
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 60 which is characterized by a cold-reacting IgG antibody capable of fixing complement.
Characteristics of Agglutinins in Hemolytic Anemia
Warm-Reacting Cold-Reacting Antibodies Antibodies
Immunoglobulin IgG IgM (Ig) class
IgM (rare) IgG (PCH only)
IgA (usually with IgG)
Optimal 37°C <30°C, usually <10°C reactivity
Mechanism of Extravascular Intravascular: hemolysis Attachment of complement-mediated membrane-bound IgG or lysis C3b to macrophage Extravascular: receptors attachment of membrane-bound C3b to macrophage receptors
Specificity Usually broad specificity Usually autoanti-I anti-Rh
Occasionally autoanti-i
PCH: autoanti-P
PCH = paroxysmal cold hemoglobinuria
A third category, mixed-type autoimmune hemolytic anemia, demonstrates both warm-reacting (IgG) autoantibodies and cold-reacting (IgM)
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 61 autoantibodies. Drugs that attach to the erythrocyte membrane or alter it in some way can cause drug-induced hemolysis.
Historically, several different mechanisms of hemolysis have been hypothesized based on whether the drug binds directly to the cell, reacts with an antibody in the circulation to form an immune complex that binds to the cell, or alters the erythrocyte antigens to stimulate formation of autoantibodies. Now, however, these antibodies are broadly classified as either drug dependent or drug independent based on reactions of patient’s erythrocytes and the drug in in vitro test systems.
Autoimmune hemolytic anemia occurs as a result of antibody development to an erythrocyte antigen that the individual lacks. When an individual is exposed to erythrocytes from another person, there could be antigens on the transfused cells that are not present on the recipient’s erythrocytes. Therefore, the recipient’s lymphocytes recognize antigens on the transfused cells as foreign and stimulate the production of antibodies (alloantibodies).
In contrast to autoantibodies, these alloantibodies react only with the antigens on the transfused cells or cells from individuals who possess the antigen. The alloantibodies do not react with the individual’s own erythrocytes. Examples of alloimmune hemolytic anemia are: Hemolytic disease of the fetus and newborn (FDFN) in which the mother makes antibodies against antigens on the fetal erythrocytes. Transfusion reactions in which the recipient makes antibodies to antigens on the transfused (donor) cells.
The presence of alloantibodies can be detected in vitro by performing an antibody screen in which the patient’s serum reacts with commercial
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 62 erythrocytes containing most of the clinically significant antigens. An autocontrol consisting of the patient’s serum and erythrocytes can also be set up. When only alloantibodies are present, the autocontrol shows no hemolysis or agglutination whereas the mixture of the patient’s serum and the commercial cells produce agglutination and (in rare cases) hemolysis.
Erythrocytes
Erythrocyte life span can be significantly shortened if the cell is intrinsically defective (intracorpuscular defect). Hemolytic anemia has been associated with defective erythrocyte membranes, structurally abnormal hemoglobins (hemoglobinopathies), defective globin synthesis (thalassemias), and deficiencies of erythrocyte enzymes. Almost all of these defects are hereditary.
An erythrocyte membrane that is normal in both structure and function is essential to the survival of the cell. Composed of proteins and lipids, the membrane is responsible for maintaining stability and the normal discoid shape of the cell, preserving cell deformability, and retaining selective permeability. Erythrocytes that have normal hemoglobin structure, enzymes, and membranes can be prematurely destroyed by factors extrinsic to the cell. This destruction can be immune-mediated via antibodies and/or complement. However nonimmune factors also can cause either extravascular or intravascular hemolysis, depending on the type and extent of injury to the erythrocyte. This section discusses nonimmune causes that lead to premature erythrocyte destruction.
Erythrocytes can undergo traumatic physical injury in the peripheral circulation, resulting in the presence of schistocytes in the peripheral blood. Contact with fibrin strands or platelet aggregates in the microcirculation or
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 63 with foreign surfaces such as artificial heart valves commonly induce such damage. There are other causes of injury, including Shiga toxin from organisms such as Esherichia coli 0157:H7. Infectious agents such as Plasmodium sp. and Babesia sp. can cause injury to the erythrocytes during their intracellular life cycle. Some drugs and chemicals can cause membrane oxidant injury, leading to intravascular hemolysis or removal of the damaged cell by the spleen.
Various chemicals and drugs have been identified as possible causes of erythrocyte hemolysis; many of these are dose dependent. In addition to erythrocyte hemolysis, chemicals and drugs can also produce methemoglobinemia and cyanosis, or in some instances bone marrow aplasia.
Hemoglobinemia and hemoglobinuria can occur as a result of osmotic lysis of erythrocytes when water enters the vascular system or when inappropriate solutions are used during a blood transfusion. Some drugs known to cause hemolysis in G6PD-deficient persons can also cause hemolysis in normal persons if the dose is sufficiently high. The hemolysis mechanism is similar to that in G6PD deficiency with hemoglobin denaturation and Heinz body formation because of strong oxidants.
Anemia associated with lead poisoning is usually classified with sideroblastic anemias because the pathophysiologic and hematologic findings are similar. Lead inhibits heme synthesis, causing an accumulation of iron within mitochondria. However, lead also damages the erythrocyte membrane, which is manifested by an increase in osmotic fragility and mechanical fragility.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 64 Acquired nonimmune hemolytic anemias represent a diverse group of conditions that lead to the shortened survival of red cells by various mechanisms. Often a number of mechanisms are operative at the same time; for example, malaria leads to mechanical destruction of red cells and, in addition, immunologic factors play a role in shortened red cell survival. Classifications may be made along either causative or mechanistic lines.
Sites and Factors that Affect Hemolysis
Regardless of whether it is caused by alloantibodies or autoantibodies, hemolysis can be intravascular or extravascular, depending on the class of antibody involved and whether the complement cascade has been completely activated. Most immune-mediated hemolysis is extravascular. Erythrocytes sensitized (coated) with antibody (IgG) or complement components (i.e., C3b) attach to macrophages in the spleen or liver via macrophage receptors for the Fc portion of IgG or the C3b component of complement. These cells are then phagocytized. Intravascular hemolysis occurs if the complement cascade is activated through C9 (the membrane attack complex), resulting in lysis of the cell. The rate at which hemolysis occurs in hemolytic anemia is related to several factors.
Approach to Diagnosis of a Hemolytic State
The approach to diagnosis of a hemolytic state initially involves establishing the fact that the rate of red cell destruction is increased and then focuses on determining the cause of hemolysis. Establishing the presence of hemolysis diagnostic tests used to establish the presence of hemolysis rely on the fact that hemolysis is characterized by both increased cell destruction and increased production.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 65 Tests Reflecting Increased Red Cell Destruction
The most frequently used tests in this category are the serum unconjugated (indirect) bilirubin and serum haptoglobin determinations. The serum unconjugated bilirubin level seldom exceeds 3 to 4 mg/dL in uncomplicated hemolytic states and reflects the catabolism of heme derived from red cells phagocytosed by the reticuloendothelial system. The test is, however, relatively insensitive, as is the measurement of fecal stercobilinogen and urine urobilinogen that represents further stages in the degradation of unconjugated bilirubin by the liver. Because the unconjugated bilirubin is bound to albumin it cannot pass the glomerular filter, and the jaundice is said to be acholuric.
On the other hand, a decreased serum haptoglobin level is a very sensitive test of both intravascular and extravascular hemolysis, and reflects the rapid clearance by the reticuloendothelial system of a complex formed between liberated hemoglobin and circulatory haptoglobin. Drawbacks to the use of serum haptoglobin levels are that low levels may occur in hepatocellular disease, reflecting decreased synthesis by the liver, and that some individuals, particularly in black populations, may have a genetically determined deficiency of haptoglobin. Increased synthesis of haptoglobin in acute inflammatory states or malignancy may also mask depletion of serum haptoglobin caused by hemolysis.
Other tests that reflect increased red cell destruction, particularly if it is primarily intravascular, are those that test for the presence of hemoglobinemia, hemoglobinuria, and hemosiderinuria. The assessment of hemoglobinemia requires stringent precautions in the prevention of hemolysis during blood collection. Once the hemoglobin-binding capacity of serum haptoglobin is exceeded, hemoglobin passes through the glomerulus
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 66 as alpha–beta (αβ) chain dimers and reassociates to α2β2 tetramers in the tubule, where the hemoglobin is reabsorbed and degraded. The liberated iron is conserved as ferritin and hemosiderin. When the tubular reabsorptive capacity for hemoglobin is exceeded, hemoglobinuria ensues and is detectable by either spectroscopic examination or commercially available dipsticks that detect heme. Staining of the urine sediment for iron (i.e., with Prussian blue) will detect the hemosiderin- and ferritin-containing renal tubular cells that are sloughed several days after a hemolytic episode.
Some of the free plasma hemoglobin may be oxidized to methemoglobin with subsequent dissociation of ferriheme, which combines with albumin to form methemalbumin. Methemalbumin can be detected spectroscopically by the Schumm's test. This test is relatively insensitive and is seldom positive in mild hemolytic states. In routine practice, determination of red cell survival using Cr51-labeled red cells is seldom required to document an increased rate of red cell destruction.
Tests Reflecting Increased Red Cell Production
The compensatory bone marrow response to hemolysis results in the delivery of young red cells in the form of reticulocytes into the circulation. These young cells contain RNA, which stains supravitally with dyes such as new methylene blue or brilliant cresyl blue. The normal reticulocyte count has a range of 0.5% to 2.0%, reflecting the fact that each day approximately 1% of the red cell mass is destroyed and replaced by young red cells from the bone marrow, because red cell survival is approximately 120 days.
The reticulocyte count is always elevated in a hemolytic state in which there is a normal compensatory bone marrow response. However, a more accurate
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 67 assessment of red cell production is required, because the percentage of reticulocytes may be falsely elevated as the reticulocytes may be diluted into a lesser number of total circulating red cells. In addition, in response to the anemia, reticulocytes may leave the bone marrow prematurely and mature in the circulation for longer than the normal maturation time of 1 day, again leading to a falsely elevated reticulocyte count. These cells (so-called shift reticulocytes) are recognizable as large bluish-gray erythrocytes on Romanowsky (Wright's, Giemsa) stains.
The reticulocyte production index (RPI) corrects the hematocrit to a normal value of 45% and takes into account the maturation time of the reticulocyte at a particular hematocrit (approximately 1.0 day at a hematocrit of 45%, 1.5 days at 35%, 2.0 days at 25%, and 2.5 days at 15%).
For example, an RPI of 5.3 is calculated for a patient suspected of having a hemolytic state with the following indices: hemoglobin, 12.0 g/dL; hematocrit, 36%; reticulocyte count, 10%; shift cells present. An RPI of greater than 2.5 to 3.0 is generally regarded as indicative of a hemolytic state, but it is very important to exclude the presence of hemorrhage in a particular patient, as this too may lead to an elevated RPI. Although the RPI is probably the single most useful test to detect a hemolytic state, a cautionary note is in order, as the test may not be sensitive enough to detect mild hemolytic states.
There are four main mechanisms of drug-induced immune-mediated hemolysis that appear to be drug-specific: nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 68 1. Hapten mechanism: The drug forms an antigenic complex with a RBC membrane protein that is recognized by an antibody. Binding of the antibody to this complex on the RBC membrane leads to destruction of the RBC. Hemolysis occurs only when the drug is present. a. Laboratory studies: DAT positive for IgG. b. Examples: penicillins.
2. Immune complex mechanism: The offending drug, or its metabolite, forms an antigenic complex with a plasma protein. An anti-drug antibody (usually IgM) binds to this antigenic complex to form an immune complex that adheres to RBCs and activates complement, which leads to hemolysis. It is the most common form of drug-induced hemolysis. a. Laboratory studies: DAT positive for C3. b. Examples: quinidine, phenacetin.
3. Autoantibody mechanism: An autoantibody (IgG) is induced by the offending drug. This autoantibody is usually directed against an Rh blood group antigen. a. Laboratory studies: DAT is positive for IgG. An antibody or a positive DAT can be present in the absence of hemolysis. b. Examples: alpha-methyldopa, ibuprofen.
4. Immunogenic drug-RBC complex (in vivo sensitization) mechanism: An antibody binds to the drug (or a metabolite) that is in an immunogenic complex that is formed by the drug (or a metabolite)
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 69 associating with a specific RBC membrane antigen. The binding of the drug to the RBC antigen provides specificity for the anti-drug antibody to bind to the drug (the antibody does not bind to the RBC antigen).
Thrombocytopenia42-61
Platelets are cell fragments that function in the clotting system. Thrombopoietin helps control the number of circulating platelets by stimulating the bone marrow to produce megakaryocytes, which in turn shed platelets from their cytoplasm. Thrombopoietin is produced in the liver at a constant rate and its circulating level is determined by the extent to which circulating platelets are cleared, and possibly by bone marrow megakaryocytes. Platelets circulate for 7 to 10 days. About one third are always transiently sequestered in the spleen. The platelet count is normally 140,000 to 440,000/μL. However, the count can vary slightly according to menstrual cycle phase, decrease during near-term pregnancy (gestational thrombocytopenia), and increase in response to inflammatory cytokines (secondary, or reactive, thrombocytosis). Platelets are eventually destroyed by apoptosis, a process independent of the spleen.
Platelet disorders include 1) an abnormal increase in platelets (thrombocythemia and reactive thrombocytosis), 2) a decrease in platelets (thrombocytopenia), and 3) platelet dysfunction. Any of these conditions, even those in which platelets are increased, may cause defective formation of hemostatic plugs and bleeding. The risk of bleeding is inversely proportional to the platelet count and platelet function. When platelet function is reduced (i.e., as a result of uremia or aspirin use), the risk of bleeding increases.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 70 Platelet Count Risk of Bleeding*
≥ 50,000/μL Minimal
20,000 - 50,000/μL Minor bleeding after trauma
< 20,000/μL Spontaneous bleeding
< 5000/μL Severe, possibly life-threatening spontaneous bleeding
*Reduced platelet function (i.e., due to uremia or aspirin use) adds to risk of bleeding.
Thrombocytopenia (combination of medical terms, “thrombocyte” [platelet] and “penia” [deficiency], based upon Greek “thrombos” [clot]; “kytos” [container, with modern meaning of cell]; and “penia” [poverty]) indicates reduced platelet count numbers. Depending on its cause, thrombocytopenia can indicate increased risk of bleeding, thrombosis, and/or mortality. Causes of thrombocytopenia can be classified by mechanism and include decreased platelet production, increased splenic sequestration of platelets with normal platelet survival, increased platelet destruction or consumption (both immunologic and nonimmunologic causes), dilution of platelets, and a combination of these mechanisms. Increased splenic sequestration is suggested by splenomegaly.
A large number of drugs may cause thrombocytopenia, typically by triggering immunologic destruction. Overall, the most common specific causes of thrombocytopenia include:
Gestational thrombocytopenia
Drug-induced thrombocytopenia due to immune-mediated platelet destruction (commonly, heparin, trimethoprim/sulfamethoxazole)
Drug-induced thrombocytopenia due to dose-dependent bone marrow suppression (i.e., chemotherapeutic agents) nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 71 Thrombocytopenia accompanying systemic infection
Immune thrombocytopenia (ITP, formerly called immune thrombocytopenic purpura)
Classification of Thrombocytopenia
Cause Conditions Diminished or Aplastic anemia absent Leukemia megakaryocytes in Myelosuppressive drugs (i.e., hydroxyurea, interferon alfa-2b, bone marrow chemotherapy drugs) Paroxysmal nocturnal hemoglobinuria (some patients)
Diminished platelet Alcohol-induced thrombocytopenia production despite Bortezomib use the presence of HIV-associated thrombocytopenia megakaryocytes in Myelodysplastic syndromes (some) bone marrow Vitamin B12 or folate (folic acid) deficiency
Platelet Cirrhosis with congestive splenomegaly sequestration in Gaucher disease enlarged spleen Myelofibrosis with myeloid metaplasia
Immunologic Connective tissue disorders destruction Drug-induced thrombocytopenia HIV-associated thrombocytopenia Immune thrombocytopenia Lymphoproliferative disorders Neonatal alloimmune thrombocytopenia Post transfusion purpura
Nonimmunologic Certain systemic infections (i.e., hepatitis, Epstein-Barr virus, destruction cytomegalovirus, or dengue virus infection) Disseminated intravascular coagulation Pregnancy (gestational thrombocytopenia) Sepsis Thrombocytopenia in acute respiratory distress syndrome Thrombotic thrombocytopenic purpura–hemolytic-uremic syndrome
Dilution Massive RBC replacement or exchange transfusion (most RBC transfusions use stored RBCs that do not contain many viable platelets)
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 72 When faced with a thrombocytopenic patient, the clinician's key question will need to be: what is the probable cause of the patient's thrombocytopenia? The answer will point to the appropriate prognostic and therapeutic considerations.
Drug-induced Thrombocytopenia
Drug-induced thrombocytopenia (DIT) is a relatively common clinical disorder. It is imperative to provide rapid identification and removal of the offending agent before clinically significant bleeding or, in the case of heparin, thrombosis occurs. DIT can be distinguished from idiopathic thrombocytopenic purpura (ITP), a bleeding disorder caused by thrombocytopenia not associated with a systemic disease, based on the history of drug ingestion or injection and laboratory findings. DIT disorders can be a consequence of decreased platelet production (bone marrow suppression) or accelerated platelet destruction (especially immune- mediated destruction).
The best-known drug associated with thrombocytopenia is heparin, which can cause mild to moderate thrombocytopenia (platelet count 50-150x109 per liter). Occurring in the first 5-10 days, this reaction involves a complex immune reaction; the diagnosis is made by one or more clinical events and antibody detection. Heparin should be immediately discontinued, and medical consult sought.
A more severe and serious heparin-induced thrombocytopenia, which occurs in around 2 per cent of patients, is linked to thrombotic events such as myocardial infarction (MI) and strokes. Glycoprotein IIb/IIIa inhibitors, such as abciximab, have also been associated with thrombocytopenia. Beta- lactam antibiotics have been associated with a seven-fold increase in risk for nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 73 thrombocytopenia, by either an immune mediated mechanism or bone marrow suppression. However, others have suggested this may be a result of confounding by indication – where the infection that the antibiotic is used to treat is an early manifestation of a blood disease. A number of other drugs have been associated with thrombocytopenia, including co- trimoxazole, acetazolamide, chlorpropamide, furosemide, diazepam, methyldopa, sodium valproate, thiazide diuretics, tolbutamide and trimethoprim.
Clinical Features
Clinically, these patients will present with moderate to severe thrombocytopenia (defined as a platelet count of less than 50x109/L) and spontaneous bleeding varying from simple ecchymoses, petechiae and mucosal bleeding to life-threatening spontaneous intracranial hemorrhage. Exclusion of other causes of thrombocytopenia (such as congenital disorders and inflammatory processes), anamnestic analysis (such as a temporal relationship between the administration of the putative drug and the development of thrombocytopenia), recurrence of thrombocytopenia following reexposure to the drug and laboratory investigation (such as, total blood count and platelet serology tests) are all important factors for the differential diagnosis. Moreover, pseudothrombocytopenia, an artifactual clumping of platelets in vitro without clinical significance, should also be ruled out.
The frequency of DIT in acutely ill patients has been reported to be approximately 19–25%. Generally, platelet count falls rapidly within 2–3 days of taking a drug that has been taken previously, or 7 or more days after starting a new drug. When the drug is stopped, the platelet count rises rapidly within 1–10 days of withdrawal. Thus, the primary treatment for nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 74 drug-induced thrombocytopenia is to discontinue the suspected causative agent. Patients experiencing life-threatening bleeding may benefit from intravenous immunoglobulin (IVIG) therapy, plasmapheresis, or platelet transfusions. Corticosteroids seem inefficient in the treatment of DIT.
Etiology
Hundreds of drugs have been implicated in the pathogenesis of DIT. As noted, DIT disorders can be a consequence of decreased platelet production or accelerated platelet destruction. A decrease in platelet production is usually attributable to a generalized myelosuppression, a common and anticipated adverse effect of cytotoxic chemotherapy. In addition, it has been reported that some chemotherapeutic agents can induce thrombocytopenia secondary to an immune-mediated mechanism.
Selective suppression of megakaryocyte production, mediated by thiazide diuretics, ethanol and tolbutamide, could lead to isolated thrombocytopenia. However, thiazides can also induce severe thrombocytopenia secondary to an immune-mediated mechanism. Accelerated platelet destruction in the presence of the offending drug is most often of immune origin. Non-immune platelet destruction, associated to a small number of antineoplastic agents such as bleomycin, can occur in thrombotic microangiopathy (TMA) and its variant form, hemolytic uremic syndrome (HUS), Immune-mediated platelet consumption is associated with a large number of drugs leading to drug- induced immunologic thrombocytopenia (DITP) by a number of different mechanisms.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 75 Mechanisms Of Drug-Induced Immunologic Thrombocytopenia
Drug-induced immunologic thrombocytopenia (DITP) is a relatively common and sometimes a serious clinical disorder characterized by drug-dependent antibodies (DDAbs) that bind to platelets and cause their destruction. Antibodies associated with DITP are unusual in that they typically bind to glycoproteins (GPs) on the cell membrane of the platelets only in the presence of the provocative drug.
In the past twenty years, much has been learned about the pathogenesis of DITP. However, knowledge of the molecular nature of the immune response is far from complete. It is also unknown how drugs induce the development of such antibodies. Following the observation that drug-dependent antibodies bind to platelets via their Fab regions, subsequent studies have documented the mechanisms of drug-dependent antibody formation.
Hundreds of drugs have been implicated in its pathogenesis, among those, drugs most often associated with DITP are: heparin, cinchona alkaloid derivatives (quinine and quinidine), penicillin, sulfonamides, non-steroidal anti-inflammatory drugs (NSAIDs), anticonvulsants, antirheumatic and oral antidiabetic drugs, gold salts, diuretics, rifampicin and ranitidine; several other drugs are occasionally described in case reports of thrombocytopenia. Quinidine and quinine appear to cause this condition more often than other medications, with the exception of heparin. Commonly used drugs that occasionally induce thrombocytopenia include:
Heparin
Quinine
Trimethoprim/sulfamethoxazole
Glycoprotein IIb/IIIa inhibitors (i.e., abciximab, eptifibatide, tirofiban)
Hydrochlorothiazide
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 76 Carbamazepine
Acetaminophen
Chlorpropamide
Ranitidine
Rifampin
Vancomycin
Hapten-Induced Karl Landsteiner’s pioneering studies in the in the field of immunochemistry in the 1930's, showed that small molecules, such Antibody as drugs, organic compounds, peptides and oligosaccharides with a molecular weight of less than 2–5 kDa are not capable of inducing an immune response. Conversely, these small molecules, called haptens, could induce an immune response when covalently attached to a carrier protein. Penicillin and penicillin derivatives are an example of this category.
Penicillins constitute a large family of compounds whose common structural basis is a beta-lactam ring condensed to a thiazolidine ring. In the presence of free amino groups of proteins the beta- lactam ring opens up and the penicilloyl group covalently links to epsilon-amino groups of lysine residues of proteins. Covalent linkage of the drug to the protein can perturb in different ways the antigen processing of proteins, therefore eliciting an immune response.
Hapten-dependent immune hemolytic anemia is a well-documented occurrence during therapy with penicillin. However thrombocytopenia induced by the “hapten” mechanism is a rare event.
Drug-Dependent Antibody binding to the platelets is the causative mechanism. These antibodies are heterogeneous and directed toward different Antibody epitopes on major platelet membranes glycoproteins (GPs), most (“Compound” or often GPIb/IX, GPV and GPIIb/IIIa and platelet-endothelial cell adhesion molecule-1 (PECAM-1) only when drug is present in “Conformational- soluble form. Dependent” Remarkably, antibodies in an individual patient are often highly Antibody) specific for a single GP. Quinine and quinidine are the most common causative drugs, but many other medications, including sulfonamide antibiotics and drug metabolites are implicated in the pathogenesis.The target of these antibodies appears to be either a “compound” epitope, made of the drug bound noncovalently (drugs are easily dissociated from platelets by in vitro washing procedures.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 77 Demonstration of drug-dependent antibodies requires the continual presence of the suspected drug during the reaction) to one or multiple site of the platelet GPs, or a conformational change elsewhere on the GP molecule that is created in the presence of the offending drug in soluble form. An alternative, but perhaps less likely possibility, is that the drug may react first with an existing antibody to induce a conformational change in the antibody binding site itself. Finally, the existence of a drug-specific antibody has been recently reported that directly recognizes quinine itself in a subset of patients experiencing quinine-induced immune thrombocytopenia.
The epitopes recognized by antibodies from patients with quinine- and sulfonamide-induced thrombocytopenia have been characterized for selected target molecules. Precise localization, however, has been achieved only for a limited number of quinine- dependent antibodies shown to bind to a restricted 70 amino acid domain of GPIIIa located just N-terminal from a well-defined disulfide-bonded region that is resistant to protease digestion and further restricted to a 17-amino acid sequence (AA residues 50– 66).
The binding site of a quinine-dependent antibody specific for GPIb (alpha subunit) has been mapped to an 11 amino acid sequence (AA residues 283–293) of the glycoprotein. Furthermore, it has been reported that Arg110 and Gln115 of GPIX are important in the formation of the quinine-dependent anti-GPIX antibody-binding site. There is also evidence that within GPIX there exists a site that is favored not only by quinine but also by rifampicin- and ranitidine- induced antibodies. Platelet-reactive antibodies induced by sulfonamide antibiotics were reported to react almost exclusively with epitopes displayed only on the intact GPIIb-IIIa complex. Overall, the immunologic specificity appears not to be important in the explanation and/or prediction of the pathogenesis and gravity of DITP.
GPIIb-IIIa Thrombocytopenia associated with GPIIb/IIIa inhibitors, such as tirofiban, eptifibatide and abciximab is a well-recognized entity. Inhibitors Thrombocytopenia is even more common with the oral GPIIb/IIIa inhibitors.
Tirofiban and eptifibatide are synthetic compounds that mimic or contain the Ang-Gly-Asp (RGD) motif and bind tightly to the RGD recognition site in GPIIb/IIIa (ligand-mimetic GPIIb/IIIa inhibitors); abciximab is a Fab fragment, of the chimeric human-murine monoclonal antibody 7E3, specific for an epitope on GPIIIa. The onset of acute thrombocytopenia within hours of the first exposure to a GPIIb-IIIa inhibitor suggested that nonimmune factors might be responsible. However, it has been shown that tirofiban- and eptifibatide-induced thrombocytopenia is due to antibodies specific to ligand-induced binding sites (LIBS) exposed after conformational changes in the GPIIb/IIIa molecule following binding of these ligand-mimetics. nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 78 Such DDAbs may develop following previous tirofiban (or eptifibatide) exposure or may indeed be naturally occurring and thus be associated with acute thrombocytopenia on first exposure to the drug. Similarly, severe immune-mediated thrombocytopenia can be observed within hours of a patient’s first exposure to abciximab. Delayed onset of thrombocytopenia can be ascribed to the persistence of platelet-bound abciximab for several weeks after treatment, rendering platelets susceptible to destruction by newly formed antibody.
It has been proposed that antibodies from patients with abciximab- induced thrombocytopenia recognize either murine sequences incorporated into abciximab or conformational changes induced by abciximab in GPIIb/IIIa when abciximab binds. Conversely, antibodies found in healthy individuals, that recognize enzymatic cleavage sites in human immunoglobulins, appear not capable of causing thrombocytopenia in patients who have received the drug.
Drug-Induced During the exposure to a medication, some patients make drug- dependent antibody and drug-independent antibodies Autoantibody (autoantibodies) simultaneously. Usually these autoantibodies are transient. On rare occasions, these autoantibodies can persist for a long period of time leading to a chronic autoimmune thrombocytopenic purpura (AITP) as it could be the case during the exposure to gold salts. The underlying mechanism of this immune- response is unknown. A possibility, is that the drug might alter the processing of platelet GPs in such a way that one or more peptides not ordinarily seen by the immune system, "neoantigens", are generated, thus “conventional” and “cryptic” GP-derived peptides could be presented to T cells in the context of Class II HLA.
Generation of such "cryptic" peptides through various mechanisms is an important theme in autoimmunity. In murine models, heavy metal ions such as Hg++ and Au+++ have been shown to alter processing of proteins, leading to presentation of cryptic (and immunogenic) peptides. It has been speculated that sensitivity reactions (including thrombocytopenia) seen in patients with rheumatoid arthritis who are treated with gold salts may be related to this mechanism, although other possibilities have been suggested. In several human models, protein-specific antibodies and other ligands perturb protein processing, leading to the generation of cryptic peptides recognized by T cells.
Immune It was hypothesized that antibodies causing DITP recognize circulating drug directly to form immune complexes somehow Complex reacting with platelets as "innocent bystanders" to cause their destruction. However, the putative immune complexes were never demonstrated experimentally and it was later shown that DDAbs bind to platelets via their Fab rather than Fc receptors. Indeed, a peculiar immune complex mechanism is responsible for the thrombocytopenia occurring in heparin-induced thrombocytopenia (HIT).
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 79 HIT differs from most other forms of drug-induced immune thrombocytopenia in that the responsible antibodies bind to complexes resulting from non-covalent interaction of a platelet alpha granules releasate, the CXC chemokine platelet factor 4 (PF4; CXCL4), and heparin to produce immune complexes that engage with the Fc gamma RIIA receptor on platelets and induce platelet activation, rather than merely binding to platelets to promote their destruction in the reticuloendothelial system. Paradoxically, about 10% of patients with HIT also experience life-threatening thrombosis.
Drug-induced thrombocytopenia occurs typically when a drug bound to the platelet creates a new and foreign antigen, causing an immune reaction. This disorder is indistinguishable from ITP except for the history of drug ingestion. When the drug is stopped, the platelet count typically begins to increase within 1 to 2 days and recovers to normal within 7 days.
Laboratory Diagnosis
The diagnosis of drug-induced thrombocytopenia is often empirical. In patients exposed only to a single drug, recovery after its discontinuation provides circumstantial evidence that the thrombocytopenia was caused by drug sensitivity. In vitro documentation of platelet-bound immunoglobulins, in the presence of the putative drug, provides direct evidence for the involvement of the tested drug in causing in vivo platelet destruction.
Many different methods have been used to detect the presence of DDAbs. These include the use of radiolabeled or fluorescein-labeled (platelet immunofluorescence test; PIFT) anti-IgG to detect platelet-bound immunoglobulin, enzyme-linked immunospecific assay (ELISA), flow cytometry and immunoprecipitation-Western blotting (IP-WB). ELISA and IP- WB allow assessing both the presence and specificity of DDAbs. Because the
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 80 formation of the target for DDAb occurs when the drug noncovalently associates with a specific protein, the drug must be constantly present in every step of the assay, including washing buffer. The specificity of the reaction is assessed by comparing the reactivity of the serum or plasma sample in the presence and in the absence of drug.
Flow cytometry is a rapid and highly sensitive technique for the detection of platelet-reactive antibodies induced by several drugs, including, but not limited to, quinine, quinidine and sulfamethoxazole. As noted, the ELISA techniques, while not as sensitive, facilitates identification of the target molecules with which DDAb react; these include the antigen capture ELISA assay, in which a monoclonal antibody specific for a platelet membrane glycoprotein is plated onto microtiter wells and used to capture the specific membrane glycoproteins from a platelet lysate (ACE, MAIPA) and a modified antigen capture ELISA in which the drug-dependent antibodies are first incubated in the presence or absence of drug with intact platelets, the cells containing bound antibodies then lysed in Triton X-100, and the lysate applied to a monoclonal antibody coded ELISA well.
Factors that should be considered for the failure to demonstrate DDAbs include poor solubility in an aqueous medium of some drugs; the possibility that the sensitizing agent can be a structurally modified form of the sensitizing drug resulting from in vivo metabolism; and a possible requirement that autologous cells be used for testing.
Treatment
The treatment includes stopping drugs that impair platelet function, and rarely, platelet transfusions. In patients with thrombocytopenia or platelet dysfunction, drugs that further impair platelet function, particularly
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 81 aspirin and other NSAIDs, should not be given. Patients who are already taking such drugs should consider alternative drugs, such as acetaminophen, or simply stop using them.
Patients may require platelet transfusion, but transfusions are given only in limited situations. Prophylactic transfusions are used sparingly because they may lose their effectiveness with repeated use due to the development of platelet alloantibodies. In platelet dysfunction or thrombocytopenia caused by decreased production, transfusions are reserved for patients with active bleeding, severe thrombocytopenia (i.e., platelet count < 10,000/μL), or in need of invasive procedures. In thrombocytopenia caused by platelet destruction, transfusions are reserved for life-threatening or CNS bleeding.
Heparin-Induced Thrombocytopenia
Studies have shown that between 1% and 5% of hospital patients exposed to heparin for 1 to 2 weeks develop HIT. Of patients diagnosed with HIT, approximately one-third will develop overt thrombosis and of these, about one-third will suffer amputation or death. Hence, the overall chance of serious morbidity or mortality as a result of a course of heparin therapy is about 3 per 1000. Early recognition and appropriate treatment may reduce these numbers.
Heparin is a widely used anticoagulant that can be administered intravenously (IV) or subcutaneously (SC) both to prevent thrombosis in high-risk patients and to limit progression of established thrombosis. It is also used as a flush to keep IV lines open. Heparin is often used to prevent clotting in extracorporeal circulation such as that in heart–lung bypass machines, where it is infused or even present as the anticoagulant coating within the tubing system.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 82 Heparin-induced thrombocytopenia is characterized by an unexplained decrease in platelet count, occurring 5 or more days after the initiation of heparin therapy. This lag is consistent with an immune response related to heparin administration, unless the patient has been previously exposed to heparin.
Nomenclature seen in the literature regarding this syndrome can be confusing. Over the years, various names have been used for this syndrome, such as heparin-induced thrombocytopenia with thrombosis syndrome (HITTS) and HIT type II. These terms have been used to distinguish immune-mediated HIT from the mild, non–immune-mediated thrombocytopenia, which may occur within the first few days of heparin administration. This nonimmune (also called HIT type I) thrombocytopenia resolves spontaneously and does not increase the risk for thrombosis. For the rest of this section, when the term HIT is used, it signifies the immune- mediated disorder in which there is a risk of thrombosis.
Heparin-induced thrombocytopenia may occur even when very-low- dose heparin (i.e., used in flushes to keep IV or arterial lines open) is used. The mechanism is usually immunologic. Bleeding rarely occurs, but more commonly platelets clump excessively, causing vessel obstruction, leading to paradoxical arterial and venous thromboses, which may be life threatening (i.e., thromboembolic occlusion of limb arteries, stroke, acute MI). Heparin should be stopped in any patient who becomes thrombocytopenic and develops a new thrombosis or whose platelet count decreases by more than 50%.
All heparin preparations should be stopped immediately and presumptively, and tests are done to detect antibodies to heparin bound to platelet factor.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 83 Anticoagulation with nonheparin anticoagulants (i.e., argatroban, bivalirudin, fondaparinux) is necessary at least until platelet recovery. Low molecular weight heparin (LMWH) is less immunogenic than unfractionated heparin but cannot be used to anticoagulate patients with HIT because most HIT antibodies cross-react with LMWH. Lepirudin is no longer available. Warfarin should not be substituted for heparin in patients with HIT and, if long-term anticoagulation is required, should be started only after the platelet count has recovered.
Although HIT may present with simultaneous thrombocytopenia and thrombosis, or sometimes with thrombosis preceding thrombocytopenia, the first manifestation of HIT is usually an unexplained decrease in platelet count of 30% to 50% or to less than 100 × 109/L, occurring 5 or more days (usually 5 to 8 days) after the initiation of heparin therapy. The platelet count rarely decreases to 15 × 109/L or less. The mean nadir has been reported to be approximately 60 × 109/L.
Heparin-induced thrombocytopenia can cause both venous and arterial thrombosis, but venous thrombosis occurs about four times more often. DVT, PE, lower limb arterial thrombosis, and coronary arterial thromboses may occur. Other sequelae can also be seen. Thromboses may be multiple. The occurrence of multiple arterial thromboses is sometimes referred to as white clot syndrome, because the thrombi formed in high-flow vessels have a high platelet and fibrin content and relatively few red blood cells.
Accurate diagnosis of HIT requires a high degree of suspicion on the part of the medical provider caring for the heparin-exposed patient. Recommendations for monitoring platelet counts vary, but it seems prudent to check a baseline platelet count at the initiation of heparin therapy and to
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 84 repeat platelet counts at intervals of several days. Because of the timing of the onset of HIT, particular vigilance around day 4 after initiation of heparin (day 0 being the first day of heparin administration) and for 10 days thereafter is particularly crucial. Patients who have had previous exposure to heparin may have an amnestic response and develop HIT rapidly after repeat heparin exposure. Many other causes for a decreased platelet count should be considered before rendering a diagnosis of HIT. Among these are fever, DIC, splenomegaly, and medications (other than heparin). Of note, in spite of the thrombocytopenia, HIT patients rarely have a bleeding diathesis.
If suspicion of HIT is high, all sources of heparin exposure should be discontinued immediately. Continued heparin exposure greatly increases the risk of thrombosis and LMWH should not be administered, as there is a cross-reactivity rate of 93%. Assays are available to assist in the diagnosis of HIT, but discontinuation of heparin should not wait for these results. Alternative anticoagulant therapy — direct thrombin inhibitors (hirudin analogs or argatroban) should be considered because of the high risk of thrombosis even after heparin is discontinued. Platelet count often rises rapidly after the discontinuation of heparin. The return of the platelet count to normal within 5 to 7 days of discontinuation of heparin is consistent with a diagnosis of HIT, although some have been observed to take up to a month to recover completely. As with most immune reactions, heparin antibodies may remain in the plasma for extended periods of time. However, testing should occur within 6 weeks of a thrombocytopenic event.
The risk of HIT appears to be greater in patients exposed to large amounts of heparin, such as when systemic anticoagulation is required. However, patients with exposures to very small amounts of heparin, such as that used
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 85 to keep intravenous lines from clotting when not in use, have also developed HIT.
Two types of assays are commonly used to assist in the diagnosis of HIT: functional assays and antigen assays. The antigen assays are ELISAs that use the H-PF4 complex as the target antigen to detect HIT-type immunoglobulin in the patient's serum. Serologic assays detect IgG, IgA, and IgM antibodies and have high sensitivity (more than 95%) but the specificity is low (74% to 86%). In other words, the positive predictive value of serologic assays is low but the negative predictive value is high.
Functional assays may simply look for platelet aggregation or may be a variation on a platelet aggregation method that detects products of the platelet release reaction, such as serotonin or adenosine triphosphate (ATP). These assays use the patient's serum, heparin, and donor platelets. Either bovine or porcine heparin may be used in the assays. There is no need for the laboratory to determine whether the patient has received bovine or porcine heparin.
It is important to use platelets from donors whose platelets are known to be reactive to HIT sera. It is unknown why some donors' platelets are reactive and others are not. Occasional combinations of known HIT sera and known reactive HIT-reactive platelets do not aggregate. Therefore, it has been suggested that platelets from two donors whose platelets are known to react to HIT sera should be used. If platelet aggregation occurs or if there is evidence of the release reaction only at a low concentration of heparin (0.1 U/mL), this is evidence that the patient's serum contains antibodies that activate and aggregate platelets in the presence of a therapeutic concentration of heparin.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 86 The effective management of patients with HIT is to prevent thrombosis by limiting platelet activation and thrombin generation. Stopping all heparin exposure is the most important step in preventing or limiting thrombosis in patients with HIT. However, even after cessation of heparin, the patient still has a risk of approximately one in three for developing thrombosis. LMWH should not be given to patients with HIT because of high cross-reactivity with PF4-heparin antibodies. Therefore, the use of other anticoagulants should be considered. In addition, the substitution of another anticoagulant may be beneficial in patients with an established thrombus.
Because of the risk of venous limb gangrene (distal ischemic necrosis that is present despite palpable or Doppler-identifiable arterial pulses) the oral anticoagulant warfarin sodium should not be used in a patient with HIT unless the patient is also adequately anticoagulated by another nonheparin anticoagulant for the first few days. The early warfarin-induced reduction of functioning protein C in the presence of increased thrombin generation seen in HIT, puts the patient at very high risk for this and other thrombotic complications. LMWH is also not recommended for the treatment of HIT. Although it is less likely to induce HIT once a patient has a heparin-induced antibody, exposure to LMWH carries a risk of thrombosis.
Anticoagulants available for use in HIT patients include heparinoids such as danaparoid and direct thrombin inhibitors such as hirudin, argatroban, and bivalirudin, which are discussed subsequently. The adjunctive use of medications that limit platelet function is also under investigation. Examples include glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitors such as GPI 562 and ADP receptor antagonists, clopidogrel and ticlopidine. The current recommendation for HIT patients is therapy with an alternate anticoagulant (direct thrombin inhibitors) to be followed by a transition to warfarin. The
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 87 warfarin should be started at low doses and given concurrently with direct thrombin inhibitors for 5 days until a therapeutic INR is achieved for 2 days.
Care should be taken in monitoring INR during this period, as direct thrombin inhibitors may prolong the INR. Obtaining a chromogenic X assay may help in transitioning a patient from direct thrombin inhibitors (DTI) to warfarin. Warfarin is typically continued for 3 to 6 months; however, the optimal duration of anticoagulation needs further study. Other commonly associated agents in HIT patients include: Quinine Quinidine Gold Salts Sulfonamide Antibiotics Rifampin Glycoprotein (GP) IIb/IIIa (GPIIb/IIIa) Receptor Antagonists Heparin
Summary
Medications offer lifesaving treatments for many patients, but they do not come without risks. Many medications may actually be responsible for inducing blood dyscrasias. Although medication-induced hematologic disorders are less common than other types of adverse medication reactions, they are associated with significant morbidity and mortality. Some agents cause predictable hematologic disease (i.e., antineoplastics), but others induce idiosyncratic reactions not directly related to the drugs’ pharmacology. The most common drug-induced hematologic disorders include aplastic anemia, agranulocytosis, megaloblastic anemia, hemolytic anemia, and thrombocytopenia.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 88 The incidence of idiosyncratic drug-induced hematologic disorders varies depending on the condition and the associated drug. Few epidemiologic studies have evaluated the actual incidence of these adverse reactions, but these reactions appear to be rare. Women are generally more susceptible than men to the hematologic effects of drugs. The incidence varies based on geography, which suggests that genetic differences may be important determinants of susceptibility.
The wide spectrum of drug-induced hematologic syndromes is mediated by a variety of mechanisms, including immune effects, interactions with enzymatic pathways, and direct inhibition of hematopoiesis. Providing proof that a drug causes a particular hematologic syndrome is frequently impossible. Many patients simultaneously receive multiple drugs, making it difficult to be certain of causality. As medicine advances, older drugs become obsolete and are replaced by newer formulations. Many drugs formerly associated with hematologic toxicities are no longer in common use. However, newer drugs are found to be associated with their own potential hematologic toxicities. Clinicians from a wide variety of specialties in their everyday practice need to understand the hematological consequences of drugs and be prepared for the occurrence and correction of these events in their patients.
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nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 89 1. ______is a lowered threshold to the normal pharmacological action of a drug.
a. Dyscrasia b. Intolerance c. Hypersensitivity d. Idiosyncrasy
2. True or False: Idiosyncrasy differs from intolerance in that it is not an exaggeration of the normal response; it is an abnormal response per se.
a. True b. False
3. The development of corneal opacities and retinal damage in patients treated with chloroquine as an antimalarial or for arthritis and amebiasis is an example of a drug
a. side effect. b. intolerance. c. hypersensitivity. d. overdosage.
4. The principal ions necessary for normal cell function include calcium, sodium, potassium, ______, magnesium, and hydrogen.
a. albumin b. bilirubin c. chloride d. heme
5. The main protein constituent of plasma is ______, which is the most important component in maintaining osmotic pressure.
a. intrinsic factor (IF) b. bilirubin c. heme d. albumin
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 90 6. Which of the following is a “secondary effect” of antibiotics?
a. An anaphylactoid reaction b. Avitaminosis c. Hepatic damage d. Digitalis action
7. A patient with a history of allergies is more likely to be a candidate for ______to a drug than a patient without a history of allergies.
a. intolerance b. overdosage c. hypersensitivity d. a secondary effect
8. True or False: The coagulation proteins responsible for hemostasis circulate in the blood as active enzymes until they are needed for the coagulation process.
a. True b. False
9. This process in which blood cells are produced and develop in the bone marrow is known as
a. cytopenia. b. hematopoiesis. c. pancytopenia. d. hemostasis.
10. This process in which blood cells are produced and develop in the bone marrow is known as
a. cytopenia. b. hematopoiesis. c. pancytopenia. d. hemostasis.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 91 11. ______concentration of cellular constituents in the blood, especially enzymes, can indicate abnormal cell destruction in a specific organ.
a. Increased b. Decreased c. Differentiated d. None of the above
12. ______contain the vital protein hemoglobin, which is responsible for transport of oxygen and carbon dioxide between the lungs and body tissues.
a. Platelets b. Monocytes c. Leukocytes d. Erythrocytes
13. True or False: The least mature cells are at the periphery of the erythroblastic island, and the more mature cells are closest to the center.
a. True b. False
14. Which of the cellular blood constituents pass through intact vessel walls to tissues where they defend against invading foreign pathogens?
a. Platelets b. Hemoglobin c. Leukocytes d. Erythrocytes
15. Primary lymphoid tissues consist of
a. thymus and spleen. b. lymph nodes. c. bone marrow and thymus. d. spleen and lymph nodes.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 92 16. True or False: Primary lymphoid tissues are those in which T and B cells develop from nonfunctional precursors into immunocompetent cells.
a. True b. False
17. Acute blood loss can cause erythropoietic tissue to temporarily replace
a. liver function. b. fatty tissue. c. hematopoiesis. d. chronic anemia.
18. Blood-forming tissue located between the trabeculae of spongy bone is known as
a. the trabecula. b. the spleen. c. bone marrow. d. platelets.
19. ______are located on the abluminal surface of the vascular sinuses and send long cytoplasmic processes into the stroma.
a. Fat cells b. Reticular cells c. Macrophages d. Adipocytes
20. Erythroblasts constitute ______of the marrow cells and are produced near the venous sinuses.
a. most b. 10-20% c. half d. 25–30%
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 93 21. ______cells can leave the bone marrow and travel to the thymus where they mature into T lymphocytes.
a. Macrophages b. Cortical epithelial cells c. Lymphoid progenitor d. Erythrocytes
22. Cytoplasmic processes of the megakaryocyte form long proplatelet processes that pinch off to form
a. macrophages. b. hemoglobin. c. platelets. d. lymphocytes.
23. True or False: Stromal cellular components also provide cytokines that regulate hematopoiesis.
a. True b. False
24. Some lymphoid progenitor cells remain in the bone marrow where they mature into
a. T lymphocytes. b. fat cells. c. epithelial cells. d. B lymphocytes.
25. Any change in volume of the hematopoietic tissue, as occurs in many anemias and leukemias, must be compensated for by a change in the space-occupying
a. adipocytes. b. cortical epithelial cells. c. reticular cells. d. macrophages.
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 94 26. Myeloproliferative disease, which begins as a hypercellular disease, frequently terminates in a state of aplasia (absence of hematopoietic tissue in bone marrow) in which ______replaces hematopoietic tissue.
a. fibrous tissue b. fat cells c. abnormal cells d. dendritic cells
27. Hematopoiesis in the bone marrow is called ______hematopoiesis.
a. bilobular b. epithelial c. abluminal d. medullary
28. If ______is/are found in the early stages, the diagnosis of aplastic anemia should be questioned.
a. cardiopulmonary complications b. petechial hemorrhages c. splenomegaly d. mucosal hemorrhages
29. True or False: The primary purpose of the thymus is to serve as a compartment in which T lymphocytes mature.
a. True b. False
30. The best-documented example(s) of drugs causing aplastic anemia is/are
a. the antibiotic chloramphenicol. b. the anti-inflammatory drug phenylbutazone. c. a., and b., above d. None of the above
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 95 31. True or False: The spleen is located in the upper-left quadrant of the abdomen beneath the diaphragm and to the left of the stomach and is essential to life.
a. True b. False
32. ______using cells collected from bone marrow has become a relatively common procedure and is curative in many patients with aplastic anemia.
a. HSCT (hematopoietic stem cell transplantation) b. IST (intensive immunosuppressive therapy) c. Cyclosporine d. ATG (antithymocyte globulin)
33. People who are taking certain medications such as cancer (chemotherapeutic) drugs, alkylating agents, anti-thyroid drugs, and dibenzepin compounds can be at risk for
a. aplastic anemia. b. acquired agranulocytosis. c. megaloblastic anemia. d. familial neutropenia.
34. A finding of hypersegmented neutrophils is considered highly sensitive and specific for ______.
a. hemolytic anemia. b. acquired agranulocytosis. c. megaloblastic anemia. d. aplastic anemia.
35. A hemolytic state exists when the in vivo survival of red cells
a. is lengthened. b. ceases. c. is shortened. d. None of the above
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 96 36. True or False: The best-known drug associated with thrombocytopenia is heparin.
a. True b. False
37. Heparin is a widely used ______that can be administered intravenously (IV) or subcutaneously (SC) both to prevent thrombosis in high-risk patients and to limit progression of established thrombosis.
a. antimalarial b. antidepressant c. anticoagulant d. antifungal
38. In patients with suspected drug-induced thrombocytopenia, who were exposed only to a single drug, recovery after its discontinuation is ______evidence that the thrombocytopenia was caused by drug sensitivity.
a. direct b. not c. absolute d. circumstantial
39. Platelet-reactive antibodies may be induced by several drugs, including, quinine, quinidine and sulfamethoxazole.
a. sulfamethoxazole. b. quinidine. c. quinine. d. All of the above.
40. Selective suppression of megakaryocyte production, mediated by thiazide diuretics, ethanol and ______, could lead to isolated thrombocytopenia sulfamethoxazole.
a. sulfamethoxazole b. tolbutamide c. heparin d. oral antibiotics
nursece4less.com nursece4less.com nursece4less.com nursece4less.com nursece4less.com 97 Correct Answers:
1. b 11. a 21. c 31. b
2. a 12. d 22. c 32. a
3. a 13. b 23. a 33. b
4. c 14. c 24. d 34. c
5. d 15. c 25. a 35. c
6. b 16. a 26. a 36. a
7. c 17. b 27. d 37. c
8. b 18. c 28. c 38. d
9. a 19. b 29. a 39. d
10. b 20. d 30. c 40. b
References Section
The reference section of in-text citations include published works intended as helpful material for further reading. Unpublished works and personal communications are not included in this section, although may appear within the study text.
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