TESTS: COMPLETE BLOOD CELL COUNT

A doctor takes a complete blood cell count (CBC) to check the quantity and quality of red blood cells, white blood cells and platelets — three major types of cells in the blood. A CBC count consists of six different tests.

Red Blood Cell Count

The red blood cell (RBC) count is used to determine if the number of red cells (which transport oxygen to tissues) in the blood is too high or too low. Extremely high levels of red blood cells may be a sign of a blood disorder such as polycythemia; extremely low levels may be a sign of anemia.

Hematocrit

The hematocrit test, like the RBC, is used to look for extremely high or low levels of red cells. In the hematocrit test, the doctor pricks a person's finger, and puts a drop of the person's blood into a glass tube. The tube is then spun in a machine at high speed, causing the red blood cells to sink to the bottom and leaving the liquid part of the blood at the top.

White Blood Cell Count

The white blood cell (WBC) count is used to determine if the level of white blood cells (which fight infection) is too high or too low. High or low levels of white blood cells may be a sign that you have an infection or are at increased risk of an infection. High levels of white blood cells can also indicate a blood cancer such as leukemia.

Differential Blood Cell Count

A differential blood cell count measures the amounts of the five different types of white blood cells — neutrophils, lymphocytes, monocytes, eosinophils and basophils. High or low levels of any of the different types of cells may be a sign of infection or allergies or of more serious disorders such as cancer, leukemia, heart attack or AIDS.

Hemoglobin

The hemoglobin test measures the amount of hemoglobin (the oxygen-carrying pigment that gives blood its red color). The hemoglobin test is also used to determine if levels of red blood cells are normal. A low level of hemoglobin indicates iron deficiency anemia.

Platelet Count

The platelet count measures the amount of platelets (cell fragments that enable blood to clot) in the blood. It is important to know the number of platelets if you are going to have surgery. Low platelet counts can result from leukemia and other cancers or from treatment for cancer. High platelet counts can result from bone marrow diseases or iron-deficiency anemia. Very low platelet counts can be a sign of internal bleeding.

Excerpted from: Family Medical Guide, Fourth Edition, American Medical Association, 2004.

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