At a Glance
Why Get Tested?
To determine your blood group and whether you have any blood group related antibodies (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.
A blood sample drawn from a vein in the arm.
Frequency of testing?
These tests will be performed prior to receiving a blood transfusion. Where medical treatment requires ongoing transfusions over a period of time the group and screen (and crossmatch) will be repeated every 72 hours in order to reduce the possibility of a transfusion reaction.
The Test Sample
What is being tested?
A group and screen is a group of tests that includes the ABO and RhD blood groups, a blood group antibody screen and identification of any blood group antibodies present.
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 the 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 to 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 transfusion is required it is important that the transfusion laboratory provides suitable blood. The blood selected for transfusion will usually lack the blood group that the person has an antibody against. This reduces the likelihood of a transfusion reaction occurring due to the presence of these blood group antibodies.
Further information on blood groups, antibody screens and how the tests are performed can be found in the Feature article Blood banking: Blood typing.
How is the sample collected for testing?
The group and screen is performed on a blood sample taken by a needle placed in a vein in the arm.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.