Transfusions are usually necessary when the PCV is less than 13 percent, but the severity of clinical signs is often directly correlated to the rapidity of onset of the anemia. Arbitrarily the severity of the anemia is indicated by the following PCV ranges: Low numbers of RBCs or a decreased (or low) PCV indicate anemia. Values that are significantly higher or lower than these send practitioners looking for further clues in certain directions, to wit: The normal PCV in the adult dog is 37 – 55 percent, and the normal RBC count is 5.5 – 8.5 million cells per microliter of blood. For example, when a patient has a nonregenerative anemia with no apparent cause, we will need to take a bone marrow sample, stain and identify the cells, and see if there is an identifiable problem somewhere along the normal progression of cell production. These red cell indices are used as an aid in categorizing or classifying anemias, and they can be helpful for monitoring the progress of the condition.īone marrow is the starting ground for all blood cells, so when we can’t find a reason for the lack of any one cell line, we may refer to a bone marrow analysis. Automated counters determine cell numbers, cell size (MCV), and hemoglobin concentration, and mathematically calculate the PCV, MCHC, and MCH. When using manual methods for CBC analyses, these indices are calculated from directly determined measurements (PCV, red cell count, and hemoglobin). Other red cell indices include MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin), and MCHC (mean corpuscular hemoglobin concentration). A look at the tube can also tell us if the serum is lipemic (contains excess fat, usually due to a non-fasting sample), or if there is serious liver damage (indicated by the yellowish tint that bilirubin imparts) or RBC breakdown in the blood (indicated by reddish serum). The plasma contains the enzymes and proteins that are evaluated in blood chemistry analyses, along with clotting and immune system factors and other components.Ī quick look at the blood-filled centrifugation tube used for determining the hematocrit (also known as the packed cell volume or PCV) will also reveal dramatic increases in white blood cells, when the white “cap” atop the RBCs is more than a few millimeters deep. The fluid portion (plasma or serum) makes up the remaining 50 – 60 percent of the volume of the blood. In a tube that has been centrifuged (or left to settle for a few minutes), the red cells are found at the bottom of the tube, and the combination of white cells and platelets form a thin cap atop the red cells. It is a simple task to separate the major cell types of the blood into fractions because their relative mass differs substantially. This percentage is multiplied by the total number of WBCs, and this absolute value of the cell type is compared to normal values. Using the microscope, one hundred white cells are identified, and the percentage of each cell type is recorded. The film (or blood smear) is stained with a variety of substances that help accentuate cell structures for easy identification. To start, a drop of blood is placed on a microscope slide and spread into a thin film. Thrombocytes (platelets) may also be counted, or they may be evaluated on the blood film and an estimate made for whether there are adequate numbers or not. Leukocytes (white blood cells or WBCs) and erythrocytes (red blood cells or RBCs) are counted, and their total numbers, compared to normal values, are assessed. ![]() ![]() The CBC uses the various cellular components of the blood to help define the animal’s current state of health or disease. The CBC is also one of the easiest of the specialized diagnostic tools to interpret – but, as is true of every diagnostic or treatment tool, it is not without pitfalls if we don’t understand its limitations (see “What the CBC Can’t Do,” end of article). Sequential CBCs can often give us a handle on the progression of the disease and a reasonable assessment of prognosis. ![]() I look at the CBC as the “great divider,” providing veterinarians with answers that help split our first impressions into either/or diagnostic scenarios.
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