Today's Veterinary Practice

JUL-AUG 2015

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tvpjournal.com | July/August 2015 | TodAy's VeTerinAry PrAcTice in-cLinic HeMAToLoGy Peer reviewed 45 HIGH MAGNIFICATION EVALUATION BY LINEAGE Red Blood Cells numerous red blood cell (rBc) shape changes are described in textbooks, but clinicians should focus on identifcation and interpretation of the most diagnostically specifc features that are occurring in signifcant numbers. These features are keys to screening for some of the most important red cell morphologic abnormalities, including: Anisocytosis and polychromasia are indicative of regeneration. reticulocyte counts are considered the reference standard for identifcation and quantitation of a regenerative response, but polychromasia can be used as an estimate, especially in dogs (Figure 6). A low level of polychromasia is normal. 1 Spherocytes, in large numbers, suggest immune- mediated anemia, zinc toxicity, or bee envenomation. spherocytes are characterized by loss of central pallor and increased cytoplasm density, and appear smaller than other red cells due to their shape change (Figure 6). They are easier to identify and more common in dogs than in cats, and their presence in small numbers is usually nonspecifc. Always evaluate for evidence of agglutination (Figure 3) and, if absent, a coombs test may be indicated. Heinz bodies in larger numbers (up to 75% of rBcs) are observed in feline metabolic stress, such as diabetes mellitus, hepatic lipidosis, and other conditions, generally without signifcant hemolysis; however, in dogs, even small numbers of Heinz bodies are considered pathologic. Large Heinz bodies are relatively easy to identify as knob- like extensions emerging from the margin of red cells (Figure 7), but smaller Heinz bodies can be diffcult to identify and may appear as small refractile areas of cytoplasm. staining with new methylene blue can highlight smaller Heinz bodies, as well as identify reticulocytes using a manual method. Heinz bodies form as the result of oxidative damage and can be important indicators of exposure to toxic amounts of acetaminophen, zinc, onions, garlic, and leeks, among other toxic substances. A careful history that evaluates potential exposure is critical, and radiographs to identify metal foreign bodies may be indicated. eccentrocytes—red cells with hemoglobin that has pulled away from the cell membrane—also indicate oxidative damage and may accompany Heinz bodies (Figure 8, page 46). Schistocytes, in large numbers, are often refective of vascular pathology, including potential for disseminated intravascular coagulation and hemangiosarcoma. These fragmented erythrocytes, which can occur nonspecifcally in small numbers, are also associated with fragmentation anemia (Figure 9, page 46). FIGURE 6. RBC morphology: Note anisocytosis due to presence of spherocytes ( arrows ) and polychromatophils ( arrowheads ). Normal erythrocytes have eosinophilic cytoplasm and central pallor. Spherocytes appear smaller, darker, and lack the central pallor typically noted in RBCs. Spherocytes can be diffcult to identify in feline patients because their RBCs generally lack central pallor. Additionally, in some instances, all RBCs present appear as spherocytes in dogs, which makes identifcation diffcult since typical RBCs are not present for comparison. Polychromatophils appear more basophilic and are frequently larger than typical RBCs. Wright- Giemsa stain; magnifcation, 1000×. FIGURE 7. Heinz bodies (arrows) in a cat secondary to metabolic stress. Echinocytes (arrowheads) are spiked, regularly spaced projections off the borders of RBCs. Echinocytes most frequently represent drying artifact, but are also seen with electrolyte derangements, renal disease, or secondary to snake envenomation. Wright-Giemsa stain; magnifcation, 1000×.

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