Coombs' Tests: Purpose

Anemia, which literally means no blood, refers to blood with abnormally low oxygen-carrying capacity. The hemoglobin in red blood cells carries oxygen. One of the many causes of anemia is destruction of red blood cells, a process called hemolysis (hemo means blood and lysis means disintegration). A simple blood count detects anemia. Even the test done before a blood donation can identify anemia. To detect hemolysis requires other tests. The Coombs' tests are conducted in order to determine the cause of anemia.

One characteristic of hemolysis is the autoimmune response against the body's red blood cells. Instead of protecting the body from outside agents, the immune system attacks parts of its own body with a deluge of antibodies. Autoimmunity is thought to be the cause of many collagen-vascular diseases, including rheumatoid arthritis and systemic lupus erythematosus. It is also the cause of the autoimmune hemolytic anemias. The Coombs' tests detect the antibodies responsible for the destruction of the red blood cells.

Causes of autoimmune hemolytic anemia include:

• drugs such as penicillin, methyldopa (lowers blood pressure), and quinidine (treats heart rhythm disturbances)
• cancers of the lymph system—Hodgkin's disease and lymphomas
• virus infections
• collagen-vascular diseases
• mismatched blood transfusions
• Rh incompatibility between a mother and fetus. This disease is called erythroblastosis fetalis

Many times the cause cannot be identified.

— Teresa Norris, RN