Coombs’ Test

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KEY POINTS

• The Coombs’ test is a blood test of the immune system. It can help diagnose medical problems or check to make sure blood for a transfusion will be a good match.
• A small amount of blood is taken from a finger with a fingerstick or from a vein in your arm with a needle and sent to a lab.
• Talk to your healthcare provider about what the test results mean and ask any questions you have.

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What is the Coombs’ test?

The Coombs’ test is a blood test of the immune system. There are 2 types of Coombs’ tests:

• Direct Coombs’ test (also called the direct antiglobulin test)
• Indirect Coombs’ test (also called the RBC antibody screen or indirect antiglobulin test)

Why is this test done?

The Coombs’ test checks for antibodies that may attack red blood cells. Antibodies are the proteins your immune system makes to fight infections, such as the flu and measles. The direct Coombs' test looks for antibodies that are already attached to the red blood cells. The indirect Coombs' test looks for antibodies that are free floating in the bloodstream. Many diseases and drugs can cause the antibodies to develop. They may also develop if you are exposed to foreign red blood cells, like during a blood transfusion or pregnancy.

This test may be done to help diagnose a medical problem, such as jaundice, anemia, lupus, or mononucleosis. A pregnant woman may have this test if there is a concern that her antibodies may attack her baby’s red blood cells. If you are going to have a blood transfusion, the test may be done to help check for blood that will be a good match.

How do I prepare for this test?

Usually no preparation is needed for this test.

Talk to your healthcare provider if you have any questions about the test.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

Some of the conditions that have a positive Coombs’ test result are:

• Systemic lupus erythematosus (lupus)
• Infectious mononucleosis (mono)
• Hemolytic anemia, which means that red blood cells are being destroyed or damaged by a medical problem, injury, or a medicine you are taking
• Blood transfusion incompatibility
• Mother and newborn blood incompatibility
• Syphilis
• Chronic lymphocytic leukemia

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history, physical exam, and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the results and ask questions, such as:

• If you need more tests
• What kind of treatment you might need
• What lifestyle, diet, or other changes you might need to make