Red Blood Cell Antibody

Does this test have other names?

Erythrocyte Ab, RBC antibody identification

What is this test?

This test looks for antibodies to red blood cells (RBCs) in your blood. These antibodies can cause problems during blood transfusions or, if you're pregnant, with your unborn baby.

Red blood cells fall into one of four main groups: O, A, B, or AB. Blood types can be further divided into other, minor groups. If you get blood from a person whose blood group is different from yours, your body may make antibodies against this other blood. That's because your immune system then sees the donor's blood as an "invader" and attacks it.

Most transfusion-related problems happen when a donor's blood isn't compatible with the person receiving the blood. This test finds out blood compatibility in advance of a blood transfusion.  

When you are pregnant, this test can find out whether you have RBC antibodies that might affect your fetus.  These antibodies may have formed from a blood transfusion, from an earlier pregnancy, or even from exposure to some viruses or bacteria.

If your fetus has a different blood group than yours, your immune system may also make antibodies against that "foreign" blood group.

It's important to know if you have any RBC antibodies early in your pregnancy to help your baby avoid problems like anemia or jaundice. Therapies are available if problems are detected.

Why do I need this test?

You may need this test before a blood transfusion to check your specific blood traits.

You may also have this test early in your pregnancy to check for antibodies that might affect your fetus. This is a routine blood test most often done at your first prenatal office visit.

You may also have this test if you need an emergency blood transfusion during delivery.

What other tests might I have along with this test?

You won't usually need other tests in addition to this one.

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 health care provider.

Test results before a blood transfusion will show whether your blood is compatible with the red blood cells in donor blood. If not, the blood bank will select another blood type.

Test results if you're pregnant will show whether you have RBC antibodies of the immunoglobulin G, IgG, subtype. Only this type can cross the placenta from your bloodstream and cause problems with your baby.

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?

Other factors aren't likely to affect your test results.

How do I get ready for this test?

You don't need to prepare for this test.  But 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.