Hematology Analyzers in Differential Diagnosis of Anemia in Cats

2024-02-19

Hematology analyzers play a crucial role in assessing various parameters related to red blood cells (RBCs), providing valuable insights into the diagnosis and management of anemia in cats. By examining a blood sample, veterinarians can obtain essential data for evaluating the severity, type, and potential causes of anemia.

Red Blood Cell Parameters:

Red Blood Cell Count, PCV, and Hb:
The hematocrit (PCV) represents the volume percentage of RBCs in whole blood and is commonly used to assess the severity of anemia. Reference values for PCV in cats are categorized based on the degree of anemia: mild (20-24%), moderate (15-19%), and severe (<14%). Hemoglobin (Hb) concentration, another essential parameter, can be determined using automated instruments. However, factors such as lipemia, hemolysis, or presence of bilirubinemia in the blood sample can influence Hb measurement. A simple method to assess test accuracy is to calculate Hematocrit (Ht) by multiplying Hb by 0.3.

It's important to note that while comparing detected values with "normal range values," it's crucial to recognize that such ranges may not apply universally. For instance, neonatal or pregnant animals may exhibit numerical deviations, and certain breed effects may also exist (e.g., sight hounds typically display higher PCV values and lower neutrophil counts). PCV, RBC count, and Hb all reflect red cell mass, and these three parameters are often correlated, making a simple PCV measurement a valuable clinical indicator.

Red Blood Cell Indices:

Mean Corpuscular Volume (MCV):
MCV represents the average volume of individual RBCs and provides data regarding their size. Elevated MCV values indicate macrocytosis, while decreased values suggest microcytosis. Factors such as sample refrigeration or prolonged storage can artificially increase MCV values. Macrocytosis may be observed in cases of regenerative anemia response, folate deficiency, hematopoietic abnormalities, and some cases of feline leukemia virus (FeLV) infection. Microcytosis may occur as a normal phenomenon in certain dog breeds (such as Akita, Shar Pei, Shiba Inu) or may indicate iron deficiency or portosystemic shunting.

Mean Corpuscular Volume (MCV):
MCH refers to the amount of hemoglobin contained within individual RBCs. Increased MCH values suggest hyperchromasia, while decreased values indicate hypochromasia, most commonly due to iron deficiency.

Mean Corpuscular Hemoglobin Concentration (MCHC):
MCHC represents the percentage of hemoglobin in total RBC count. A clinically significant decrease in MCHC values is noteworthy, as there is no physiological condition associated with increased MCHC values. Factors contributing to elevated MCH values include RBC lysis, lipemia, or the presence of Heinz bodies. Preparation of a quality blood smear is essential for the diagnosis of anemia.

Red blood cell morphology typically exhibits a biconcave disc shape with a central pale area. While the diameter of canine RBCs is approximately 7 mm, feline RBCs are slightly smaller (6 mm). Various morphological changes in RBCs may be observed clinically, and distinguishing them based on blood smear assessment is crucial as they provide essential diagnostic information.

Following a preliminary assessment of anemia, additional serum biochemistry tests, confirmation of medical history and clinical symptoms, or specific tests such as PCR may be conducted to further elucidate the etiology. For example, microscopic examination of fecal samples for occult blood and parasites in cats can be useful. Bone marrow evaluation is typically performed for any animals with unexplained non-regenerative anemia and may require sedation or anesthesia. While most testing equipment can obtain reliable data on RBCs and white blood cells, platelet counts may be underestimated. Therefore, microscopic examination of blood smears should ideally accompany instrument-based testing. Observing blood smear under a microscope also provides information about RBC size and appearance, aiding in determining whether anemia is regenerative or non-regenerative.