Complete blood counts (CBCs) are frequently performed because they give important information on the status of the different blood cell components. For instance, the white blood cell count is increased with many infections and in certain other conditions as well. It can also be decreased in certain infections, including some viral infections as well as a variety of other diseases. By knowing if white cell count is high, low, or normal the physician can start narrowing down the list of possible diagnoses.

A low red blood cell count indicates anemia. Once the presence of anemia is confirmed, its cause can be sought. Anemia is a very common disorder which may be due to conditions as natural as monthly menstrual bleeding or as serious as an acute hemorrhage from an as yet undiscovered colon cancer. There are numerous causes of anemia, and many individuals are anemic at some point in their lives.

Not only can a CBC document the presence of anemia, it also can give insight into its cause. There are parameters within a CBC which indicate how large or how small the red blood cells are. Some forms of anemia typically result in small cells, while others cause large cells. However, in many cases, the size of the red blood cells in anemic patients is normal.

The platelets, while not true cells, are important clotting components of the blood. As in the above cases, the platelet count can lead a doctor toward or away from a specific diagnosis.

Potential Risks: To perform a CBC, as most other blood tests, a sample of blood is obtained by puncturing a vein (usually in the arm) with a needle. This procedure is called venipuncture. Though it is certainly possible for the needle to inadvertently be introduced into a nearby artery, nerve, or tendon, routine venipuncture is generally a very safe procedure and other than an occasional bruise at the site, complications are very unusual.

Terms your physician may use when discussing this test with you:

anemia - a low concentration of red blood cells

bands - an immature population of a class of white blood cells called PMN's. Bands are released into the bloodstream prematurely when the body needs more cells to help an acute fight infection. Their presence in large numbers usually signifies a potentially serious infection.

bandemia- the presence of an excessive number of bands in the bloodstream

erythrocytes - red blood cells

hematocrit - a measure of the volume of red blood cells in the bloodstream

hemoglobin - the oxygen carrying component of red blood cells. The hemoglobin level is an indicator of the concentration of red blood cells.

leukocytes - another name for white blood cells (see below) There are different classes of leukocytes, which include the following:
polymorphonuclear leukocytes (PMNs)

leukocytosis - an increased number of circulating white blood cells

platelets - these particles are very important for blood clotting

red blood cells - the blood cells that carry oxygen to cells throughout the body

white blood cells - the blood cells which play a large role in protecting your body from infection and various other diseases.

Author's Bio: 

Dr. Ann Hester is a board certified internal medicine specialist, author, founder of and creator of the Patient Whiz. She can be reached at

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