The red cell antibody screen looks for circulating antibodies in your blood that target and destroy red blood cells other than your own. These become important to screen for if you are having a blood transfusion from a donor, or if you are pregnant. The antibodies react if you are transfused with blood that is different to yours. Screening can ensure that the donor blood is fully compatible with your own and it is safe for you to have. In pregnancy a baby can inherit red blood cells from its father that are not compatible with the mother and she may develop antibodies that can harm the developing baby.

What is being tested?

An antibody screen is commonly performed as part of a group of tests that includes ABO and RhD blood group, a blood group antibody screen and a crossmatch.

Red blood cells have chemical structures (most commonly proteins or carbohydrates) on the outside surface of the red blood cell. These chemical structures usually have a defined function such as determining the shape of the cell or assisting with transport of chemicals into, or out of, the red blood cell. In addition, they determine a person's blood group.

There are over 200 different blood groups known. The most important blood groups are the ABO and the RhD blood groups. However other blood groups can also become important. There are inherited blood group differences between people. When a person is exposed to blood groups that are different from their own the immune system may respond by producing a blood group antibody. This is very similar to the way we produce antibodies against germs (bacteria and viruses). The transfusion laboratory performs an antibody screen to detect and identify any blood group antibodies as these can cause transfusion reactions or haemolytic disease of the newborn (HDN).

If a blood transfusion is required it is important that the transfusion laboratory provides compatible blood. The blood selected will usually lack the blood group that the person has made an antibody against. This reduces the likelihood of a reaction occurring due to the presence of these red cell antibodies.

In pregnancy the obstetrician or midwife will closely monitor any blood group antibodies, to determine if treatment is required before or after delivery, in order to protect the baby from HDN.

How is it used?

Antibody screens are used to select appropriate blood for transfusion.

It is also used during and immediately after pregnancy (antenatal group and screen), to determine the risk of a baby being affected by haemolytic disease of the newborn (HDN), a condition which may lead to severe anaemia, brain damage and even death of the baby.

When is it requested?

If your doctor indicates that transfusion with blood or blood components may be required as part of your medical treatment.

If you are pregnant it will be performed during your pregnancy.

What does the result mean?

The result allows laboratory staff to select appropriate blood for transfusion and to determine whether pregnant women are at risk of their baby being affected by haemolytic disease of the newborn (HDN).

Common questions

• Do these antibodies cause me any harm?

Red cell or blood group antibodies usually only cause a problem if you are transfused, or in some cases to unborn or newborn babies. In rare cases they can cause anaemia or other problems.

• Does everybody have blood group antibodies?

Most people have blood group antibodies to the ABO blood groups. This is one reason why these are the most important blood group. However, only a small percentage of people (3-5%) have antibodies to other blood groups.