Educational Commentary – Blood Cell Id: Identifying Common Peripheral Blood Cells

EDUCATIONAL COMMENTARY – BLOOD CELL ID: IDENTIFYING COMMON PERIPHERAL BLOOD CELLS

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Learning Outcomes

On completion of this activity, the participant should be able to: • describe the significant morphologic features of common peripheral blood cells. • discuss characteristics of red blood cell and platelet morphologic variations.

Case Study

A 78 year old female was seen in the emergency room for leg pain. The CBC results are as follows: WBC=18.2 x 109/L, RBC=3.43 x 1012/L, Hgb=10.1 g/dL, Hct=35.6%, MCV=103.8 fL, MCH=29.3 pg, MCHC=28.2 g/dL, RDW=22.0%, Platelet=2615 x 109/L.

Educational Commentary

The images presented in this testing event represent normal white blood cells and platelets that may be seen in the peripheral blood. In addition, photographs of an abnormality in platelets and another with erythrocytes are presented for educational review and discussion.

The cell in Image BCI-15 is a normal lymphocyte. This is an example of a small lymphocyte, although these cells are variable in size. Small lymphocytes typically have a thin rim of blue cytoplasm. The nucleus is usually oval, round, or slightly indented, with clumped and dark purple chromatin.

American Proficiency Institute – 2014 3rd Test Event EDUCATIONAL COMMENTARY – BLOOD CELL ID: IDENTIFYING COMMON PERIPHERAL BLOOD CELLS (cont.)

Image BCI–16 shows an eosinophil. Note the distinctive and numerous red-orange cytoplasmic granules. These granules are usually large and uniform in size. Often eosinophils are bilobed, although that is not the case in this example. The nuclear chromatin appears dense and stains purple. Because eosinophils are normally present in small numbers in the peripheral blood, it is not necessary to classify them according to maturation stage.

Image BCI–17 identifies another type of granulocyte, a basophil. As with eosinophils, basophils are present in such small numbers in the peripheral blood that they do not have to be classified based on stage of maturation. The cell in this image is a typical basophil. In contrast to eosinophils, the cytoplasmic granules in basophils are dark purple, almost black. The granules are often large, round, and characteristically so numerous that they obscure the nucleus. Because basophilic granules are also water soluble, they sometimes appear faded or washed-out from the staining process.

Basophils should not be confused with neutrophils containing toxic granulation or intracellular cocci (bacteria). Toxic granules are smaller than the granules in basophils and do not overlay and hide the nucleus as is typical for basophilic granules. Likewise, bacteria will be seen only in the cytoplasm of a cell and will not obscure the nucleus. In addition, bacteria may appear not just as single organisms, but sometimes in clusters or pairs. Often, bacteria may also be seen extracellularly, which can be helpful in distinguishing them from other intracellular inclusions or granules. Another useful tip when trying to decide the identity of a cell or an inclusion is to review other cells (or images) on the peripheral blood smear. When suspecting toxic granulation or intracellular bacteria in a cell, look for other indications of infection, such as Döhle bodies, vacuolization, and immature granulocytes.

American Proficiency Institute – 2014 3rd Test Event EDUCATIONAL COMMENTARY – BLOOD CELL ID: IDENTIFYING COMMON PERIPHERAL BLOOD CELLS (cont.)

Image BCI-18 illustrates a normal platelet. Platelets originate from nucleated cells in the bone marrow called megakaryocytes and represent cytoplasmic remnants of these cells. Therefore, although platelets lack a nucleus and are therefore technically not cells, they can be called “cells” because of their derivation from megakaryocytes. Platelets are small, generally 1 to 4 µm in diameter. Their shape may vary, but they are usually round or oval. Platelets often appear granular and stain blue-gray or light purple. The platelet in this picture is morphologically typical.

Image BCI-19 shows a segmented neutrophil. Segmented neutrophils characteristically have 3 to 4 nuclear lobes that are connected by strips of chromatin. Sometimes, as in this example, the chromatin filaments may be obscured. However, the density of the chromatin and areas of parachromatin suggest that this is a mature cell. The rule of thumb when uncertain as to the maturation stage of a cell is to classify the cell as the most mature stage. The other typical feature of segmented neutrophils is the numerous pink, tan, or violet-pink cytoplasmic granules.

The arrow in Image BCI-20 identifies a giant platelet. The term giant is used to define a platelet that is larger than a normal red blood cell. Giant platelets may be round, oval, or irregularly shaped. The edges of the cell may be smooth, ruffled, or scalloped, as in this example. The cytoplasm is usually a blue-gray or light purple, like the color of a normal platelet. The cell may have no granules or, as in this platelet, may have numerous granules, either dispersed or in aggregates.

Giant platelets should not be confused with artifacts or

American Proficiency Institute – 2014 3rd Test Event EDUCATIONAL COMMENTARY – BLOOD CELL ID: IDENTIFYING COMMON PERIPHERAL BLOOD CELLS (cont.) any type of nucleated cell. One type of artifact is the smudge cell, a leukocyte that has been mechanically disrupted during the process of blood smear preparation, forming a fragile cell. The name originates from the “smudge” appearance that results when the cytoplasm disintegrates and is stripped away, leaving only nuclear material. Smudge cells have no defined size or shape, although they are often as large as or larger than white blood cells. They are often lymphocytes, because these cells are particularly susceptible to physical trauma during smear preparation. Therefore, smudge cells are a common finding in chronic lymphocytic leukemia. Likewise, smudge cells have no granules and stain red-purple.

In addition, giant platelets should be distinguished from nucleated cells such as megakaryocytes and monocytes. The concentration of granules in the center of this giant platelet suggests a nucleus. However, there is no nuclear membrane and the staining color is not the dark purple typically associated with nuclear chromatin. In fact, the overall color of this cell is similar to other platelets seen in the image. Therefore, this giant platelet should not be confused with any nucleated cell, such as a megakaryocyte or monocyte.

Image BCI-21 identifies a spherocyte. Spherocytes have a decreased surface to volume ratio because they have lost membrane. Therefore, they are smaller than normal red blood cells, are dense, and lack any area of central pallor. Spherocytes are most often seen associated with hereditary spherocytosis, immune-mediated hemolytic anemia, and microangiopathic hemolytic anemias. However, as the underlying mechanism resulting in thrombosis is not specified in this case study patient, identifying a spherocyte on the peripheral blood smear can be clinically significant. Also note that if the entire smear is scanned using API’s ImageViewer, many examples of other spherocytes as well as the giant platelet previously described may be seen.

Summary

This testing event presented images of normal and abnormal peripheral blood cells. Identification of these cells involves a systematic process evaluating all morphologic features of cells, including overall cell size, nuclear characteristics, and cytoplasmic appearance. Appropriate identification and classification of cells provides important information to help the clinician determine a diagnosis.

American Proficiency Institute – 2014 3rd Test Event