What is an RBC Antibody Screen?

An RBC (red blood cell) antibody screen is a blood test that looks for RBC antibodies in your blood. These antibodies destroy red blood cells that are different from your own (foreign). Having RBC antibodies won't harm your health, but:

• If you have a blood transfusion, they could cause serious illness.
• If you are pregnant, they could harm your baby.

Antibodies are proteins that your immune system makes to attack germs and other foreign substances in your body, including some foreign red blood cells. Blood transfusions and pregnancy are two ways that you may come into contact with foreign red blood cells.

Your immune system reacts to foreign red blood cells when they have markers, called antigens, that are unlike the antigens on your own cells. The unfamiliar antigens trigger your immune system to make RBC antibodies to destroy the foreign red blood cells.

An RBC antibody screen can find these antibodies before they cause health problems.

Other names: antibody screen, indirect antiglobulin test, indirect anti-human globulin test, IAT, indirect coombs test, erythrocyte Ab, RBC antibody identification

What is it used for?

An RBC antibody screen is used to check your blood for RBC antibodies before you have a blood transfusion or when you're pregnant:

• Before a blood transfusion, the test can help show whether donor blood is compatible (well matched) with your blood. If your blood has antibodies to the donor blood, your immune system will attack the red blood cells in the transfusion. This type of immune reaction can make you seriously ill. An RBC antibody screen helps match you to blood that won't cause a harmful reaction.

• During pregnancy, the test can show whether you have RBC antibodies that could attack your unborn baby's red blood cells, causing a very serious type of anemia in the baby. Antibodies that may cause this problem in pregnancy, include Rh antibodies and Kell antibodies.

  The most common cause of anemia in babies is called Rh incompatibility. Rh factor is a red blood cell antigen that you inherit from your parents. If you don't have Rh antigens on your blood cells, but your unborn baby does, then you have Rh incompatibility. If your blood mixes with your baby's blood, you will make RBC antibodies that attack your baby's blood.

  Early in your pregnancy, or even before you're pregnant, you'll have a prenatal blood test to find out whether you have the Rh antigen:

  • If you don't have Rh antigens, you are Rh-negative. If the baby's biological father is Rh-positive (has Rh antigens), or their blood type is unknown, you will be treated as if you and your baby have Rh incompatibility. That's because most people are Rh positive.

    Usually, Rh incompatibility doesn't cause problems in your first pregnancy. That's because it takes time for your body to make antibodies, and exposure to the baby's blood mostly happens during childbirth, if at all. But Rh antibodies could cause problems in future pregnancies, or if you need a blood transfusion.

    An RBC antibody screen checks whether you've made antibodies that could affect your current pregnancy or a future pregnancy. If you haven't made any, you may have treatment that will prevent your body from making Rh antibodies.

  • If you have Rh antigens, you are Rh positive. Your immune system will not make Rh antibodies, so you won't have Rh incompatibility. But you may still have an RBC antibody screen to look for other less common red blood cell antibodies that could also affect your baby.

An RBC antibody screen may also look for antibodies to Kell antigens. Kell antigens are a group of red blood cell antigens that can trigger a strong immune response if you don't have Kell antigens in your own blood.

In most cases, Kell RBC antibodies develop over time after exposure through several blood transfusions. But you may also make Kell RBC antibodies during pregnancy if your baby has Kell antigens and you don't. Kell antibodies can cause a very severe anemia that may be life-threatening for an unborn baby.

Why do I need an RBC antibody screen?

Your health care provider may order an RBC screen if you need a blood transfusion or if you're pregnant. An RBC antibody screen is usually done in early pregnancy, as part of routine prenatal testing. If you have Rh-negative blood, you may need to have another RBC antibody screen later in your pregnancy.

What happens during an RBC antibody screen?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for an RBC screen.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If you are getting a blood transfusion: The RBC screen results will help identify the type of donor blood that best matches yours:

• A positive result means you have one or more RBC antibodies in your blood that could attack red blood cells in certain types of donor blood. You will likely need more tests to find out exactly what type of RBC antibodies you have. This information will help find donor blood that won't trigger your immune system to destroy the red blood cells in the transfusion.
• A negative result means no RBC antibodies were found.

If you are pregnant: The RBC screen will show whether your blood has any antibodies that could harm your baby.

• A negative result means that no RBC antibodies were found. If you have Rh-negative blood, you may be given an injection (shot) to prevent your body from making Rh antibodies that could harm your current baby or a baby in a future pregnancy.
• A positive test result means that you have RBC antibodies in your blood. You will likely need more tests to find out what type of RBC antibodies you have.
  • If you have Rh antibodies, you may have more frequent tests during your pregnancy to check the health of your baby.
  • If you have other RBC antibodies, but not Rh antibodies, your pregnancy will be closely watched. If you have Rh-negative blood, you may still have an injection to prevent your body from making Rh antibodies that could harm this baby or a baby in a future pregnancy.

If you have questions about your results, talk with your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an RBC antibody screen?

Rh incompatibility is not common. Most people are Rh positive, which does not cause blood incompatibility and poses no health risks.

Once you have RBC antibodies, they never go away. But you may have too few to show up on a test. If have had an RBC antibody screen that showed you have RBC antibodies, make sure to tell your provider, especially if you need a blood transfusion or are pregnant.