Antibody Tests (Coombs Test)

Coombs' Test, Indirect Coombs' Test

Results

Antibody tests are done to find antibodies that attack red blood cells.

Normal

No antibodies are found. This is called a negative test result.

• Direct Coombs test. A negative test result means that your blood does not have antibodies attached to your red blood cells.
• Indirect Coombs test. A negative test result means that your blood is compatible with the blood you are to receive by transfusion. A negative indirect Coombs test for Rh factor (Rh antibody titer) in a pregnant woman means that she has not developed antibodies against the Rh-positive blood of her baby. This means that Rh sensitization has not occurred.

Abnormal

• Direct Coombs test. A positive result means your blood has antibodies that fight against red blood cells. This can be caused by a transfusion of incompatible blood or may be related to conditions such as hemolytic anemia, systemic lupus erythematosus (SLE), hemolytic disease of the newborn (HDN), lymphoma, mycoplasma infection, advanced stage cancer, or infectious mononucleosis.
• Indirect Coombs test. A positive test result means that your blood is incompatible with the donor's blood and you cannot receive blood from that person. If the Rh antibody titer test is positive in a woman who is pregnant or is planning to become pregnant, it means that she has antibodies against Rh-positive blood (Rh sensitization). She will be tested early in pregnancy to check the blood type of her baby. If the baby has Rh-positive blood, the mother will be watched closely throughout the pregnancy to prevent problems to the baby's red blood cells. If sensitization has not occurred, it can be prevented by a shot of Rh immunoglobulin.

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Author:	Maria G. Essig, MS, ELS	Last Updated: June 12, 2008
Medical Review:	Anne C. Poinier, MD - Internal Medicine W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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