Indirect Coombs test, Coombs test (indirect), blood antibody screening, IAT
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.
You may have this blood test before you get a blood transfusion. Doctors 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.
Your doctor 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.
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 health care 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 indicate your blood and the donor's blood are incompatible. A positive test result during pregnancy could mean your baby has hemolytic disease.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
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.
Some drugs, including insulin and penicillin, could interfere with your test results. Other medications that can affect your results include drugs to treat tuberculosis and drugs to control heart rhythm, blood pressure, or seizures.
You don't need to prepare for this test. In addition to the specific medications mentioned above, be sure your doctor 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.