ASK THE VET (complete blood count, or CBC)
by Linda Pesek, DVM
Westbury Animal Hospital
319 Union Avenue
Westbury, NY
516-333-1123
This article first appeared in the October 1993 issue of SQUAWK, the publication of the Big Apple Bird Association and and is reprinted with permission. This article is one in a continuing series which describes diagnostic tests performed by the avian vet.
In previous columns, I have discussed the importance of a health exam and a Psittacosis test. Today, I would like to talk about the importance of a complete blood count, or CBC.
Blood collection can be done by venipuncture from the jugular vein in the neck, the cutaneous ulnar vein in the wing, the caudal tibial vein in the leg, or from a toe nail. The volume of blood which can be safely removed from a bird depends on the size of the bird and on its health status. Normal, healthy birds can lose 10% of their blood volume without a problem. (The total blood volume of a bird is approximately 10% of its body weight.)
Modern instrumentation enables a large number of tests to be run on a relatively small sample of blood.
The erythrocyte, or red blood cell, of birds is important in carrying oxygen to the tissues and in removing waste materials. Red blood cells are produced in the yolk sac and bone marrow of the embryo, and in the marrow of the adult bird.
Erythrocytes of birds differ from those of mammals in that they are oval shaped and have a nucleus. The number of erythrocytes varies with the age, sex, hormonal influence, and environment. Evaluation of the erythrocyte number can allow the veterinarian to determine if a normal number or too few, red blood cells are present. A normal hematocrit (PCV) is between 35-55. A packed cell volume (PCV) under 35 indicates that anemia (too few red blood cells) is present. This can occur as a result of blood loss or hemorrhage due to trauma or parasites, increased red blood cell destruction, or decreased red blood cell production. Anemia can also be the result of chronic disease such as chlamydiasis (Psittacosis), aspergillosis, tuberculosis or liver disease.
Too high a red blood cell number is often associated with dehydration.
White blood cells, or leukocytes, are produced mainly in the bone marrow. Avian leukograms vary between normal individuals of the same species and with repeated sampling from the same bird. Age, environment and daily fluctuations influence the white blood cell counts. Five types of white blood cells exist: heterophils, eosinaphils, basophils, lymphocytes and menocytes. The heterophil is the most numerous of the white blood cells and it has an important function in fighting disease.
An elevated white blood cell count, or leukocytosis, can occur with infection, inflammation, and tissue death or necrosis.
A decreased white blood cell count, or leukopenia, can occur as a result of an overwhelming infection, or exposure to toxins and chemicals.
Repeated leukograms, or white blood cell counts, are very helpful in evaluating an avian patient's progress.
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