Patient education: Red blood cell antibody screening (The Basics)

What are red blood cell antigens and antibodies? — Red blood cells, or "RBCs," are the blood cells that carry oxygen around the body.

Everyone's RBCs are a little different. Because of this, the immune system can consider another person's RBCs as foreign. If this happens, the immune system can react by forming "antibodies."

●Antibodies are proteins the body makes when it recognizes something as foreign.

●Antigens are the things on the RBCs that the antibodies recognize. They are made of proteins and sugars. Each person has their own set of RBC antigens depending on what they inherited from their parents. For example:

•The "ABO" blood group is 1 type of RBC antigen. You inherit the A antigen, B antigen, or neither from each of your parents. If you have "type O" blood, it means that you do not have any A or B antigens. Other possible combinations are 1 or 2 copies of A, 1 or 2 copies of B, or 1 of A and 1 of B.

•"RhD" is another type of RBC antigen. Sometimes, it is simply called "Rh." You are either positive for it or negative.

•There are other RBC antigens, too.

Whichever antigens you do not have, your body can make antibodies to them.

Why does the immune system make antibodies? — Usually, your immune system makes antibodies after it has been exposed to something foreign. It does this to try to protect you the next time you are exposed to that thing. This is how vaccines work.

For RBC antigens:

●For the A and B antigens, you make antibodies naturally.

Someone who has type O blood will make antibodies to both A and B. Someone who is type A will make antibodies to B. Someone who is type B will make antibodies to A. And someone who is type AB will not make antibodies to either. Type AB is very rare.

●For other RBC antigens, you only make antibodies if your blood is exposed to someone else's blood. The main ways this can happen are:

•You get a blood transfusion.

•You share needles.

•You get pregnant – When you are pregnant, the fetus can have antigens inherited from the father. Sometimes, you get exposed to the baby's blood during birth. You could also get exposed even if the pregnancy ends before a baby is born.

What is RBC antibody screening? — This is a blood test to check your blood type and whether you have certain RBC antibodies. It is done by testing a sample of your blood.

The test can look for antibodies against many different RBC antigens. Some of the important ones are A, B, and RhD. If your blood cells do not have A, B, or RhD, your blood type is "O negative." Screening can also check for antibodies against other RBC antigens.

Why might I get RBC antibody screening? — The main reasons are if:

●You need a blood transfusion – This means receiving blood donated by another person.

If you need a blood transfusion, the blood bank will test your blood first to see if you have any antibodies to RBC antigens. They will give you blood that is a good match for your blood type. If there is not enough time to test your blood, they will give you "type O" blood.

●You are pregnant – Screening can show if you have antibodies to antigens on your baby's RBCs. When this happens, it can cause problems for the fetus or for the baby after birth. This is called "hemolytic disease of the fetus and newborn." It can cause severe anemia (low RBC count) in the fetus or the baby.

The results of screening will help your doctor plan your care.

What does the screening test show? — A screening test checks your blood type and whether you have antibodies to some of the common RBC antigens.

If your blood has antibodies against RBC antigens, this is called a "positive" antibody screen.

●If you need a blood transfusion, the blood bank will give you blood that does not have these antigens.

●If you are pregnant, it depends which antibodies you have and whether the fetus might have the antigen(s).

•Your doctor will test the baby's father for RBC antigens, if possible. This helps figure out if the baby might have the RBC antigen. If this does not give a clear answer, the doctor can do other tests to learn more about the baby's blood.

•If your baby does have the RBC antigen, your doctor will monitor you closely for the rest of your pregnancy. Doctors can do tests for signs of anemia in the baby. If the tests show that there are problems, the medical team can make a plan for treatment. This might include transfusions before or after the baby is born.

Is there a way to prevent RBC antibodies from forming? — Not always. But for pregnant people whose blood type is RhD-negative, there is a treatment that can prevent the body from making antibodies to RhD. This is given as a shot during the pregnancy.

The only other ways to stop RBC antibodies from being made are to avoid sharing needles and avoid transfusions if they are not needed. Doctors know to avoid giving you blood unless you really need it.

More on this topic

Patient education: Blood type test (The Basics)
Patient education: Blood transfusion (The Basics)
Patient education: Pregnancy in Rh-negative people (The Basics)
Patient education: Prenatal care (The Basics)

Patient education: Blood donation and transfusion (Beyond the Basics)