Summary
If you need to have a blood transfusion it is essential that you are given blood that is similar or compatible to your own to prevent reactions to the transfusion and potentially a severe illness. Your blood group needs to be identified and your blood tested to see whether you have any antibodies to blood group antigens. The major blood groups are ABO and RhD. When the laboratory has this information it can decide which is the right type of blood to give you.
Why get tested?
The ABO blood typing system
Your blood group depends on the type you inherit from your parents.
Blood is grouped according to the ABO typing system. There are four ABO blood groups: A, B, AB and O. Each blood group can be either RhD positive or RhD negative, which means in total there are eight different combinations of ABO and RhD blood groups.
If you have the A antigen on your red cells your blood is called type or group A. If you have the B antigen you are group B. If you have both the A and B antigens your group is AB while anyone without either antigen is group O, the most common ABO group in Australia.
RhD antigens
Transfusion reactions take place when you are given blood that contains antigens not present on your blood cells and antibodies in your body recognise these as foreign and mount a response.
Before you have a transfusion the laboratory determines which antigens are present on your red cells and then selects blood that is compatible, safe, and avoids a transfusion reaction.
Blood group | Corresponding antibodies |
A | Have Anti-B antibodies circulating in their blood |
B | Have Anti-A antibodies circulating in their blood. |
AB | Have neither Anti-A or Anti-B antibodies circulating in their blood |
O | Have both Anti-A and Anti-B antibodies circulating in their blood. |
An important blood group antigen is the D antigen known as RhD. If it is present on your cells, you are RhD Positive and if it is absent you are RhD Negative.
The RhD antigen is also important if you are pregnant. If you are RhD negative but the father is RhD positive the unborn baby may also be RhD positive. Sometimes RhD negative mothers may produce antibodies to the RhD antigen if the unborn baby is RhD positive. This antibody is known as anti-D and can cause destruction of foetal and neonatal red cells, known as haemolytic disease of the foetus and newborn (HDFN).
To prevent RhD negative mothers producing anti-D antibodies, prophylactic RhD immune globulin injections are given routinely during pregnancy.
Other antigens
There are many other antigens present on blood cells — more than 200 different groups are known. There may be circumstances where you have developed antibodies to some of these antigens and therefore if you are to be transfused you will need to receive blood without the antigen that has generated the antibodies. For more information about this see Blood group antibody screen.
Having the test
Sample
Blood
Any preparation?
None
Your results
Your results will show whether you are A, B, AB or O and if you are Rh negative or positive.
| Blood group including RhD type | Compatible blood groups for transfusion |
| A positive | A positive or negative, O positive or negative |
| A negative | A negative, O negative |
| B positive | B positive or negative, O positive or negative |
| B negative | B negative, O negative |
| AB positive | AB positive or negative, A positive or negative, B positive or negative, O positive or negative |
| AB negative | AB negative, A negative, B negative, O negative |
| O positive | O positive or negative |
| O negative | O negative |
If you are Blood Group AB you are a universal recipient and can be given blood of any type because you have both antigens and there will be no reaction to group A, B or AB blood.
Questions to ask your doctor
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
More information
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