Coombs test

A Coombs test is a type of antibody test. It checks your blood for 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 cause them to be destroyed.

This test is used to:

• Test blood before a transfusion.
• Find antibodies caused by disease or a blood transfusion.
• Check a newborn baby with Rh-positive blood if the person who gave birth has Rh-negative blood.
• Check to see if a person who is pregnant has Rh-positive or Rh-negative blood.

A health professional uses a needle to take a blood sample, usually from the arm.

In general, there's nothing you have to do before this test, unless your doctor tells you to.

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 someone who is pregnant means that they have not developed antibodies against the Rh-positive blood of the baby. This means thatRh sensitizationhas not occurred.

Direct Coombs test.A positive result means that your blood has antibodies that fight against red blood cells. This can be caused by a transfusion of incompatible blood. Or it may be related to conditions such as autoimmune hemolytic anemia orhemolytic disease of the newborn(HDN).

• Indirect Coombs test.A positive test result means that your blood is incompatible with the donor's blood and you can't receive blood from that person. If the Rh antibody titer test is positive in someone who is pregnant or is planning to become pregnant, it means that they have antibodies against Rh-positive blood (Rh sensitization). The person will be tested early in pregnancy to check the blood type of the baby. If the baby has Rh-positive blood, the person 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.