feline-evaluation of the feline erythron health and disease

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Vol . 19, No. 3 March 1997 Continuing Education Article Refereed Peer Review FOCAL POINT KEY FACTS 5Mechanisms of anemia in cats are often multifactorial; determining the mechanism in a particular case can be difficult. Evaluation of the Feline Erythron in Health and Disease Kansas State University Mosette Eibert, DVM David C. Lewis, BVSc, PhD T he feline erythron has several unusual features; veterinarians must be cautious when applying their general knowledge of red blood cell (RBC) physiology and metabolism to feline patients. This article de- scribes features that are unique to the feline erythron and explains how they impact the interpretation of RBC data in cats. GENERAL REQUIREMENTS Evaluation of the feline erythron includes quantitative and qualitative assess- ments. Quantitative data provided by commercial laboratories include the RBC count, hematocrit (HCT) or packed cell volume (PCV), hemoglobin concentration, mean corpuscular volume (MCV), mean corpuscular hemo- globin concentration (MCHC), and RBC distribution width (RDW). Quanti- tative buffy coat analyzers measure the PCV and hemoglobin concentration, from which the MCHC c an be calculated. Qualitative evaluation of RBCs (via examination of a blood smear) complements quantitative analysis. Examina- tion for parasitized cells and for changes in RBC shape, size, and staining qual- ity may provide valuable diagnostic information. Technicians who evaluate blood smears should be familiar with feline RBC morphology . SAMPLE COLLECTION AND HANDLING  Jugular venipuncture enables reliable, rapid collection of an adequate blood volume for complete analysis. Ethylenediaminetetraacetic acid, or EDTA (the blood collection tube with the lavender top) is the preferred anticoagulant. To minimize blood loss from small cats and those that require multiple sampling, small blood collection tubes (2.0- or 0.5-ml draw) are preferable. Tubes should be filled to the recommended capacity to ensure the proper blood:anticoagu- lant ratio. Blood should be gently mixed with anticoagulant. Dilution of a sample with EDTA due to underfilling causes RBC shrinkage; the results are spuriously decreased HCT and MCV and increased MCHC. 1 Blood smears should be made immediately after venipuncture, using nonanti- s Morphologically abnormal RBCs are inefficiently removed by the feline spleen and thus are often encountered on blood smears. s Only aggregate reticulocytes need to be counted in cats with moderate to marked anemia; in cats with mild anemia, punctate reticulocytes also should be enumerated. s Anemia associated with chronic disease in cats can develop within 3 days; the hematocrit can reach as low as 15%. s Feline red blood cells are prone to oxidative damage and Heinz body–induced hemolysis.

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