The Laboratory Diagnosis of Platelet Disorders an Algorithmic Approach
Total Page：16
File Type：pdf, Size：1020Kb
CAP Laboratory Improvement Programs The Laboratory Diagnosis of Platelet Disorders An Algorithmic Approach Kandice Kottke-Marchant, MD, PhD; George Corcoran, MD; for the College of American Pathologists Coagulation Resource Committee c Objective.ÐTo provide both a detailed description of the count. Multiple laboratory procedures can now be used to laboratory tests available in the diagnosis of platelet dis- determine the underlying pathologic condition of platelet orders and a testing algorithm, based on platelet count, dysfunction when other de®ciencies or defects of the co- that can be used to direct the evaluation of platelet dis- agulation cascade or ®brinolysis are ruled out. Simple pro- orders. cedures, such as platelet count, peripheral blood smear, Data Sources.ÐA literature search was conducted using and a platelet function screening test, will often lead the the National Library of Medicine database. investigator to more speci®c analyses. Although platelet Study Selection.ÐThe literature on laboratory testing of function testing is often limited to larger medical centers platelet function was reviewed. with highly trained technologists, newer technologies are Data Extraction and Data Synthesis.ÐBased on the lit- being developed to simplify current procedures and make erature review, an algorithm for platelet testing was de- platelet function testing more accessible. This review pro- veloped. vides an algorithm for platelet testing that may be of ben- Conclusions.ÐA history of mucocutaneous bleeding of- e®t to pathologists and physicians who deal with hemo- ten indicates abnormal platelet function that can be asso- static disorders. ciated with a normal, increased, or decreased platelet (Arch Pathol Lab Med. 2002;126:133±146) latelets are small (2-mm-diameter), nonnucleated blood VWF, thrombospondin, and laminin,4 many of which are P cells produced in the bone marrow from megakar- ligands for receptors on the platelet surface. These adhe- yocytes. Platelets are activated rapidly after blood vessel sive proteins are exposed when the endothelial layer is injury or blood exposure to the arti®cial surfaces of im- disrupted. Because of the large number of extracellular planted devices, and they are a crucial component of the matrix proteins and a high density of platelet surface re- primary hemostatic response. In their inactivated state, ceptors, platelet adhesion to areas of vascular injury is ex- platelets are roughly discoid in shape and contain cyto- tremely rapid. VWF, a large, multimetric protein secreted plasmic organelles, cytoskeletal elements, invaginating into the extracellular matrix from endothelial cells, facili- open-canalicular membrane systems, and platelet-speci®c tates platelet adhesion by binding to platelet surface gly- granules, called alpha and dense granules. Platelets have coprotein Ib/IX/V, especially at high shear rates.5±7 Plate- numerous intrinsic glycoproteins embedded in the outer lets can also adhere to vascular wall±associated ®brin or surface of their plasma membrane that are receptors for ®brinogen through interaction with platelet surface gly- ligands ranging from ®brinogen, collagen, thrombin, and coprotein IIb/IIIa.8,9 thrombospondin to von Willebrand factor (VWF) and ®- After adhering to the subendothelium, platelets under- bronectin.1±3 Platelets promote hemostasis by 4 intercon- go a cytoskeletal activation that leads to a shape change nected mechanisms: (1) adhering to sites of vascular injury with development of pseudopods. Intracellular signaling or arti®cial surfaces, (2) releasing compounds from their processes lead to increased cytoplasmic calcium and then granules, (3) aggregating together to form a hemostatic initiate a secretory release reaction, whereby products from platelet plug, and (4) providing a procoagulant surface for the alpha granules (platelet factor 4, b-thromboglobulin, activated coagulation protein complexes on their phospho- thrombospondin, platelet-derived growth factor, ®brino- lipid membranes (Figure 1). gen, VWF) and dense granules (adenosine diphosphate Platelet adhesion to the subendothelium is the initial step [ADP], serotonin) are released into the surrounding mi- in platelet activation. The subendothelium is composed of lieu.10 The granule membranes contain many integral gly- extracellular matrix proteins, such as collagen, ®bronectin, coproteins on their inner lea¯et, such as P-selectin (CD62p) in the alpha granule and gp53 (CD63) in the ly- sosome, which become expressed on the outer platelet Accepted for publication September 7, 2001. membrane after the release reaction.11 The release of ADP From the Department of Clinical Pathology, The Cleveland Clinic from the dense granules, together with calcium mobili- Foundation, Cleveland, Ohio. Reprints: Kandice Kottke-Marchant, MD, PhD, Department of Clini- zation, leads to a conformational change of the ®brinogen cal Pathology, The Cleveland Clinic Foundation, L30, 9500 Euclid Ave, receptor, the glycoprotein IIb/IIIa receptor complex (in- 12 Cleveland, OH 44195 (e-mail: [email protected]). tegrin aIIbb3). This conformational change of the ®brino- Arch Pathol Lab MedÐVol 126, February 2002 Laboratory Diagnosis of Platelet DisordersÐKottke-Marchant et al 133 Figure 1. Platelet activation is stimulated by vascular injury through exposure of platelets to extracellular matrix proteins and adsorbed plasma proteins, including von Willebrand factor (VWF) and ®brinogen (Fib). Platelets adhere to VWF through the surface glycoprotein Ib/IX/V and to ®brinogen through the glycoprotein IIb/IIIa receptor. Platelet adhesion stimulates intracellular signaling, leading to degranulation of alpha granules (platelet factor 4 [PF4] and b-thromboglobulin [bTG]), and phospholipid reorganization with formation of coagulation complexes and ®brin formation. Adenosine diphosphate (ADP) release from dense granules and activation of the glycoprotein IIb/IIIa receptor also occur, leading to aggregation of platelets to the adherent layer. gen receptor initiates the process of aggregation, whereby duration, pattern, and severity of bleeding problems, in- a glycoprotein IIb/IIIa receptor on one platelet is bound cluding whether the bleeding is spontaneous or associated in a homotypic fashion to the same receptor on adjacent with trauma or surgery. A lifelong bleeding diathesis may platelets via a central ®brinogen molecular bridge. Beside suggest a congenital platelet dysfunction, but an onset in ADP, other agonists, such as epinephrine, thrombin, col- adulthood does not necessarily exclude a congenital prob- lagen, and platelet-activating factor, can initiate platelet lem. In obtaining a history of bleeding pattern, it is nec- aggregation by interaction with membrane receptors. This essary to determine whether a true hemorrhagic disorder platelet release reaction and aggregation lead to the re- exists. In this regard, it is often helpful to assess if the cruitment of many other platelets to the vessel wall with bleeding is out of proportion to the degree of trauma, or the formation of a hemostatic platelet plug. whether blood transfusions were required for relatively Activated platelets also play a vital procoagulant role that minor surgical procedures, such as tooth extractions. serves as a link between platelet function and coagulation Platelet-mediated bleeding disorders usually result in a activation. Platelet membrane phospholipids undergo a re- mucocutaneous bleeding pattern, with ecchymosis, pete- arrangement during activation with a transfer of phos- chiae, purpura, epistaxis, and gingival bleeding commonly phatidyl serine from the inner table to the outer table of observed.4 This pattern is in contrast to that observed with the platelet membrane, providing a binding site for phos- coagulation protein disorders, in which deep tissue bleed- pholipid-dependent coagulation complexes that activate ing and hemarthroses are more common. Von Willebrand both factor X and prothrombin.13 disease, an abnormality of VWF, has bleeding symptoms LABORATORY TESTS USED IN THE EVALUATION OF very similar to platelet dysfunction, and evaluation for von PLATELET FUNCTION Willebrand disease should be included in the initial eval- uation of a possible platelet disorder.14 Bleeding diatheses Clinical History due to vascular malformations may give a bleeding pat- A careful clinical and family bleeding history should be tern similar to platelet disorders, but is often more focal taken before beginning a laboratory evaluation of platelet than diffuse. Acquired purpuras, such as those seen with function. The history should include an assessment of the disseminated intravascular coagulation, vasculitis, or in- 134 Arch Pathol Lab MedÐVol 126, February 2002 Laboratory Diagnosis of Platelet DisordersÐKottke-Marchant et al Table 1. Drugs That Affect Platelet Function* Nonsteroidal anti-in¯ammatory drugs (NSAIDs) Psychotropics and anesthetics Aspirin Tricyclic antidepressants (ie, imipramine) Ibuprofen Phenothiazines (ie, chlorpromazine) Mefenamic acid Local and general anasthesia (ie, halothane) Indomethacin Chemotherapeutic agents Cox-2 inhibitors Mithramycin Antimicrobials Daunorubicin Penicillins Carmustine Cephalosporin Miscellaneous agents Nitrofurantoin Hydroxychloroquine Dextrans Amphotericin Radiographic contrast Quinidine Cardiovascular agents Ethanol b -Adrenergic blockers (ie, propanol) Foods Vasodilators (ie, nitropursside, nitroglycerin) Diuretics (ie, furosemide) Caffeine Calcium channel blockers Garlic Cumin Anticoagulants Turmeric Heparin