Blood types are based on the proteins (antigens) on the surface of red blood cells (RBCs). The major antigens are the A, B and Rh. Blood group test detects the antigens and is used to determine the ABO blood group and Rh type.
In short, people with both antigens are blood group AB, those with no antigens are blood group O and those with A or B only are blood group A or B respectively. If the Rh protein is present the status will be positive and if absent negative. The blood group will thus be reported e.g. A+ (having A and Rh antigens present).
There naturally antibodies formed against the antigens NOT present on the red blood cells, e.g. a person with blood type A will have anti-B antibodies against B antigens and a person who is type B will have anti-A antibodies directed against the A antigens. If blood type AB, the patient will have neither of these antibodies, compared to blood type O who will have both. This is very important when considering a blood transfusion because if a patient has antibodies to e.g. B antigens they will not be able to receive donor blood of the B blood group because the antibodies will destroy the red cells from the donated blood as it recognises it as foreign to the body. It remains important that donated blood is matched correctly.
Rh antibodies develop when person is Rh factor negative is exposed blood that is Rh positive. This usually occurs during pregnancy (mother is Rh negative and the baby is Rh positive) or during a blood transfusion. The first exposure is usually not that strong but subsequent exposure e.g. following pregnancies might have severe reactions to the baby.
Blood group testing establish whether a person is blood group A, B, AB, or O and Rh positive or Rh negative.
This test is typically used:
Blood group testing is typically performed on all donated blood and blood recipients (Transfusion)
Some conditions that may require a blood transfusion include:
Rh status is required as part of the pre-natal work-up during pregnancy. When the mother is known to be Rh negative, the new-born is screen to determine incompatibility and associated risks and appropriate preventative measures.