At a Glance
Why Get Tested?
To determine your blood group in preparation for a possible blood transfusion or treatment with specific blood components or products.
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.
A blood sample drawn from a vein in the arm or a finger-prick or heel-prick (newborns).
Frequency of testing?
Your blood group will be determined 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.
Test Preparation Needed?
The Test Sample
What is being tested?
A blood group is commonly performed as part of a group of tests. These tests include ABO and RhD blood groups, a blood group antibody screen and a crossmatch.
Blood groups are 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 ones are the ABO and the RhD blood groups. These are routinely determined prior to transfusion and during pregnancy. These two blood group systems also determine the eight most common blood types: A Positive, A Negative, O Positive, O Negative, B Positive, B Negative, AB Positive and AB Negative.
Further information on blood groups and how the tests are performed can be found in the Features article on Blood banking: Blood typing.
The ABO blood groups are extremely important when receiving a blood transfusion. There are some blood groups (e.g. group O Negative, the ‘universal donor’) that can be given to almost any other person. However other blood groups (e.g. group AB) must only be transfused to people of the same blood group in order to prevent a potentially fatal transfusion reaction.
How is the sample collected for testing?
The blood group is performed on a blood sample taken by a needle placed in a vein in the arm or by a finger-prick (for children and adults) or heel-prick (for infants).
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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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.