Antibody Tests (Coombs Test)

Coombs' Test, Indirect Coombs' Test

Test Overview

Antibody tests are done to find certain antibodies that attack red blood cells. Antibodies are proteins made by the immune system. Normally, antibodies bind to foreign substances, such as bacteria and viruses, and destroy them.

The following conditions cause antibodies to be made.

Transfusion reaction

Human blood is typed by certain markers (called antigens) on the surface of red blood cells . If you get a blood transfusion, the transfused blood must match your type; that is, it must have the same antigens as your red blood cells. If you get a transfusion of blood with antigens different from yours (incompatible blood), your immune system destroys the transfused blood cells. This is called a transfusion reaction and can cause serious illness or even death. This is why matching blood type is so important.

Rh sensitization

Rh is an antigen. The full name for this antigen is Rhesus factor.

If a pregnant woman with Rh-negative blood has a baby (fetus) with Rh-positive blood, Rh sensitization may occur. The baby may have Rh-positive blood if the father has Rh-positive blood. Rh sensitization happens when the baby's blood mixes with the mother's blood during pregnancy or delivery. This causes the mother's immune system to make antibodies against the baby's red blood cells in future pregnancies. This antibody response is called Rh sensitization and, depending on when it happens, can destroy the red blood cells of the baby before or after it is born. If sensitization happens, a fetus or newborn can develop mild to severe problems (called Rh disease or erythroblastosis fetalis). In rare cases, if Rh disease is not treated, the fetus or newborn may die.

A woman with Rh-negative blood can get a shot of Rh immunoglobulin (such as RhoGAM) that almost always stops sensitization from occurring. Problems from Rh sensitization have become very rare since Rh immunoglobulin was developed.

Autoimmune hemolytic anemia

A type of hemolytic anemia called autoimmune hemolytic anemia is a rare disease that causes antibodies to be made against a person's own red blood cells.

Two blood tests can check for antibodies that attack red blood cells: the direct Coombs test and the indirect Coombs test. The direct Coombs test is done on a sample of red blood cells from the body. It detects antibodies that are already attached to red blood cells. The indirect Coombs test is done on a sample of the liquid part of the blood (serum). It detects antibodies that are present in the bloodstream and could bind to certain red blood cells, leading to problems if blood mixing occurs.

	Go to top of page	Go to next section
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
© 1995-2010 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.