Does this test have other names?

Indirect Coombs test, Coombs test (indirect), blood antibody screening, IAT

What is this test?

This test looks for antibodies in your bloodstream. Antibodies are proteins that your immune system makes in response to possible foreign tissue or germs in your body. If you receive a blood transfusion, these antibodies could attach to donated red blood cells and damage them. This can lead to a transfusion reaction.

Why do I need this test?

You may need this blood test before you get a blood transfusion. Healthcare providers need to know if your blood has antibodies that may harm a donor's red blood cells.

If you do not have antibodies to the donor's red blood cells, you can have the blood transfusion safely.

If you have antibodies, the blood will clump (agglutinate) and can't be used.

You might also have this test if you are pregnant. It could be a problem for the baby if your blood cells lack a surface protein called D antigen, but your baby has inherited the D antigen from the other parent. (Having the protein is also called being Rh-positive, while lacking the protein is Rh-negative.)

In this case, your body will make antibodies against the D antigen in your baby’s blood. This can cause your baby to develop a severe type of anemia called hemolytic disease. This happens more often with a second child, not the firstborn.

The test can be done on your blood before the baby is born. Afterward, it can be done on blood from the umbilical cord and from your baby.

What other tests might I have along with this test?

You may also need a direct antiglobulin test. This test might be needed if antibodies are found in the indirect antiglobulin test or if you have a reaction to a blood transfusion.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

A negative test result means you do not have antibodies to donor red blood cells, and the blood is not clumping.

A positive test result could mean your blood and the donor's blood are not compatible. A positive test result during pregnancy could mean your baby has hemolytic disease.

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.

What might affect my test results?

Many medicines could interfere with your test results. Be sure to ask your healthcare provider if you need to stop taking any of these medicines before the test.

How do I get ready for this test?

You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.