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Interpreting of blood work in small ruminants (Proceedings)

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Aug 01, 2011

A complete blood count can be an important extension of the physical examination in ruminants and may be used to suggest certain disease processes when exam findings are vague and is useful for establishing a prognosis in many cases.


Normal Complete Blood Count Values for Cattle, Sheep and Goats
Whole blood in EDTA is the preferred sample, with the vacuum volume of the tube fully replaced by the sample. An unstained, air-dried blood film should be made within 15 minutes of collection and submitted with the remaining sample in the tube for laboratory analysis if the time to analysis is greater than 2 hours. An accurate CBC can be achieved in properly stored samples in tubes up to 24 hours. If platelet counts are of particular importance, those counts should be made within 4-6 hours. If samples are to be shipped to an outside laboratory, they should be wrapped in packing material to protect from breakage and shipped on ice. Automated analyzers must be properly calibrated for the species of interest and stained smears should undergo manual examination.

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Red blood cell parameters

A complete evaluation of RBCs should include a PCV and/or hematocrit (HCT), RBC count, hemoglobin (Hgb), MCV, and MCHC, RBC morphology and parasites.

The PCV is determined by centrifugation of a microhematocrit tube and determination of the percentage of RBCs per volume of blood. This is easily performed in-clinic. The HCT is a calculated value based on RBC size and number

The MCV, MCH, and MCHC are characteristics of the RBCs, indicating average cell size, average cell hemoglobin content and average cell hemoglobin concentration, respectively. MCV may be calculated, but most instruments directly measure red cell volume, reporting the mean. A decreased MCV is termed microcytosis; increased MCV is macrocytosis and normal MCV is normocytosis. Note that many microcytes or macrocytes must be present to change the MCV since it is a mean value.

There are also two cellular hemoglobin measurements reported by many automated analyzers, MCHC and MCH. The MCHC is considered the more useful of the two cellular hemoglobin measurements, and is a calculated value. Descriptive terms relative to MCHC are normochromic, hypochromic or hyperchromic for normal, decreased and increased cellular hemoglobin concentrations, respectively. The most common cause of a slightly decreased MCHC is a strongly regenerative anemia, because immature red cells (polychromatophils) contain less than a full complement of hemoglobin. Iron deficiency anemia may also cause a decreased MCHC, and hypochromasia (pale red cells) may be visible on the blood film.