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The Coombs test looks for antibodies that may stick to your red blood cells and cause red blood cells to die too early.
Direct antiglobulin test; Indirect antiglobulin test
A blood sample is needed.
No special preparation is necessary for this test.
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
There are two types of the Coombs test:
The direct Coombs test is used to detect antibodies that are stuck to the surface of red blood cells. Many diseases and drugs can cause this. These antibodies sometimes destroy red blood cells and cause anemia. Your doctor may order this test if you have signs or symptoms of anemia or jaundice.
The indirect Coombs test looks for free-flowing antibodies against certain red blood cells. It is is most often done to determine if you may have a reaction to a blood transfusion.
A normal result means there was no clumping of cells (agglutination). This means you have no antibodies to red blood cells.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
An abnormal (positive) direct Coombs test means you have antibodies that act against your red blood cells. This may be due to:
The test may also be abnormal without any clear cause, especially among the elderly.
An abnormal (positive) indirect Coombs test means you have antibodies that will act against red blood cells your body views as foreign. This may suggest:
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Elghetany MT, Banki K. Erythrocytic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 32.