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Indirect Antiglobulin

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 circulating in your bloodstream. Antibodies are proteins that your immune system makes in response to a possible foreign invader. If you receive a blood transfusion, these antibodies could attach to donated red blood cells and damage them.

Why do I need this test?

You may have this blood test before you get a blood transfusion. Healthcare providers need to know if your blood has antibodies that aren't compatible with a donor's red blood cells.

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

If you do have incompatible antibodies, the blood will agglutinate (clump) 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 father. (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 that could cause baby to develop a severe type of anemia called hemolytic disease. This usually happens 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 the baby.

What other tests might I have along with this test?

Your healthcare provider may also order a direct Coombs test. This test might be needed if antibodies are found in the indirect Coombs test or if you have a reaction to a transfusion.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

A normal finding is negative. This 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 incompatible. A positive test result during pregnancy could mean your baby has hemolytic disease.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly 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. In addition to the specific medicines mentioned above, 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 illicit drugs you may use. 

Medical Reviewers:

  • Moloney Johns, Amanda, PA-C, MPAS, BBA
  • Snyder, Mandy, APRN