Skip to main content
URMC / Encyclopedia / Content

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 1 of 4 main groups: O, A, B, or AB. Blood types can be further divided into other, minor groups. Each blood type is also identified as being positive or negative, depending on the presence or absence of the Rh factor. 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 getting 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 found.

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?

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.

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 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?

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. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you take. This includes medicines that don't need a prescription and any illegal drugs you may use.

Medical Reviewers:

  • Chad Haldeman-Englert MD
  • Raymond Turley Jr PA-C
  • Tara Novick BSN MSN