At a glance

Also known as

Blood group antibody screen; Indirect Coombs test; Indirect antiglobulin test; Ab Sc

Why get tested?

To determine whether you have any blood group or red cell antibodies that need to be considered by the transfusion laboratory prior to a possible blood transfusion.

When to get tested?

If your doctor indicates that transfusion with blood or blood components may be required as part of your medical treatment, or as part of antenatal screening undertaken during pregnancy.

Sample required?

A blood sample drawn from a vein in the arm.

Frequency of testing

Your antibody screen will be performed prior to receiving a blood transfusion. Where medical treatment requires ongoing transfusions over a period of time, a group of tests (group and screen, crossmatch) will be repeated every 72 hours in order to reduce the possibility of a transfusion reaction.

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.

Further information on blood groups, antibody screens and how the tests are performed can be found in Blood banking.

How is the sample collected for testing?

The antibody screen is performed on a blood sample taken by a needle placed in a vein in the arm.

The Test

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 test 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.

Last Review Date: March 1, 2017