Finding the right tests…
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Finding the right tests…
Haematology
Blood group testing tells you which of the eight common blood types you carry - A, B, AB or O, each either Rh-positive or Rh-negative. A lab mixes your blood with antibodies against type A and type B; whichever ones make your cells clump reveal your ABO group, and a separate reaction confirms your Rh factor. Knowing your group matters most before a transfusion or surgery, where the wrong type can trigger a dangerous reaction, and during pregnancy, where an Rh-negative mother carrying an Rh-positive baby needs specific monitoring to prevent newborn jaundice or anaemia. It is also checked before organ or bone marrow donation.
The test reports two results together: your ABO group (A, B, AB or O) and your Rh factor (positive or negative), giving one of eight combinations such as O-positive or AB-negative. It is read from how your red cells react when mixed with known antibodies - cells that clump have reacted, cells that stay separate have not. A confirmatory back-typing step, mixing your serum against known A and B cells, is usually run alongside it before any transfusion.
Your ABO group and Rh factor together decide which donated blood you can safely receive. O-negative blood can go to almost anyone in an emergency, which is why it is called the universal donor type, while AB-positive people can receive from any group. A mismatched transfusion makes your immune system attack the donated cells, which can be serious.
If a mother is Rh-negative and her baby is Rh-positive, her body can start making antibodies against the baby's blood cells, usually from a later pregnancy onward if untreated. This is why blood group and Rh testing is done early in pregnancy - an injection given at the right time prevents the antibodies from forming in the first place.
- Before any blood transfusion - Before major surgery, in case transfusion becomes necessary - During pregnancy check-ups - Before organ, tissue or bone marrow donation or transplant - When registering to donate blood
Your blood group does not change over your lifetime, so once it is confirmed and recorded, you generally do not need to repeat the test unless a hospital needs it verified again before a procedure.
There are four ABO groups - A, B, AB and O - each further split into Rh-positive or Rh-negative, giving eight possible combinations such as O-positive or AB-negative. Your report will state your exact combination.
No, it is fixed by your genes and stays the same throughout your life, with rare exceptions such as after a bone marrow transplant from a donor with a different group. You do not need to repeat this test regularly.
If an Rh-negative mother carries an Rh-positive baby, her immune system can react against the baby's blood cells. Early testing lets doctors give a preventive injection at the right time, which has made this complication far less common.
People with O-negative blood are often called universal donors. Their red cells lack the markers that most immune systems react against, which makes that blood usable in emergencies across other groups.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
No special preparation is usually needed for blood typing. Ask your doctor or the centre if other tests are being drawn at the same visit, since those might have their own rules.
A sample of your blood is mixed with antibodies against type A and type B blood, and whichever ones cause the cells to clump reveal your ABO group. A separate test then confirms whether the Rh protein is present.