Coombs’ Test

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KEY POINTS

• The Coombs’ test is a blood test of the immune system. It can help diagnose certain 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 child’s arm with a needle and sent to a lab. Your child's healthcare provider may make a tiny cut in the baby's heel to get a small amount of blood to test.
• 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 the 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 your child is exposed to foreign red blood cells such as during a blood transfusion.

This test may be done to help diagnose a medical problem such as jaundice, anemia, lupus, or mononucleosis. A newborn may have this test if there is a concern that the mother’s antibodies may attack the baby’s red blood cells. If your child is 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 my child 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?

A small amount of blood is taken from a finger with a fingerstick or from a vein in your child’s arm with a needle. Your child's healthcare provider may make a tiny cut in the baby's heel to get a small amount of blood to test. 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 child’s 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 your child is taking
• Blood transfusion incompatibility
• Mother and newborn blood incompatibility
• Syphilis
• Chronic lymphocytic leukemia

What if my child’s test result is not normal?

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

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