Complete Blood Count (CBC) in Dogs
A complete blood count (CBC) is a blood test used to measure and evaluate cells that circulate in the blood. The test includes an actual counting of red and white blood cells as well as an analysis of cells viewed on a blood smear. A CBC is indicated in any ill animal. The test is often done prior to anesthesia to evaluate overall health. A CBC may be useful as a screening test for underlying infection, anemia and illness. There are no real contraindications to performing this test, but care should be taken if the pet has a tendency to bleed excessively.
What Does a CBC Reveal?
A CBC will reveal the presence of anemia (low red blood cell count). The results can indicate a possible diagnosis of infection, inflammation, or immune system disease. Sometimes, the CBC can help determine the underlying cause of an anemia or infection. Drugs that affect the bone marrow change the CBC. Certain types of cancers, especially leukemia, may be evident on a blood smear. Blood parasites and some microorganisms are found by careful inspection of the blood cells during the CBC. In some cases, the results of the CBC will prompt your veterinarian to recommend other diagnostic tests.
How Is a CBC Done?
As with a person, blood must be obtained from a superficial vein with a sterile needle and collection syringe or container. Either the external jugular (neck) vein or a superficial leg vein will be sampled. The pet is held gently by an assistant and positioned to allow access to the vein. At a minimum, the hair is wetted with alcohol to better reveal the vein. A small bit of hair may need to be clipped over the puncture site, especially in pets with long hair or small veins. After obtaining the blood sample, the puncture site is gently pressed and later checked to insure there is no excessive bleeding or swelling. This inspection also should be done at home since rarely the puncture site may ooze blood under the skin, especially in pets with fragile veins or clotting problems.
After the blood sample is drawn, it is placed immediately into a special glass tube that contains an anti-coagulant. Many veterinary hospitals have automated machines and can perform the test in the clinic. Other veterinarians rely on outside reference laboratories. The analysis is done using an expensive and sophisticated computer device that determines the number and type of cells present in the blood. Generally a report is given for red blood cells, white blood cells, and platelets. The instrument also can determine the amount of hemoglobin (iron pigment), the size of the red blood cells, and how much hemoglobin is within each.
After the blood is sent through the machine, a drop of blood is placed on a microscope slide. This sample is then stained with specific biologic dyes. A laboratory technician evaluates the blood cells under a microscope. The various types of white blood cells are counted and the blood machine results are confirmed. Any abnormalities of the cell shape, size or numbers is detected and reported.
A complete blood count generally takes about 30 to 60 minutes to complete, once the blood has reached the laboratory. Results are typically available in 6 to 24 hours.
Is a CBC Painful?
Any pain involved is associated with the collection of the blood sample. A small needle is used to pierce the skin and enter the blood vessel. As with people, the pain experienced from a hypodermic needle will vary among individual animals. In most cases it is a brief "prick" and many pets don't register any obvious response to the procedure.
Is Sedation or Anesthesia Needed for a CBC?
Neither sedation nor anesthesia is needed in the vast majority of patients; however, some pets resent the needle stick or the restraint. In these cases, tranquilization or ultrashort anesthesia may be needed to obtain the samples.