Blood Groups
ABO Groups - The ABO group system is encoded by polymorphic carbohydrate antigens on the surface of RBCs. RBCs can have either one of antigen A or antigen B, or both antigens (i.e. AB) or no antigens (i.e. O). People naturally form antibodies against the A or B antigen not present on RBCs, which are present within their plasma. Someone with group O red cells, has antibodies against both anti-A and anti-B in their plasma. The ABO group of donor blood must be matched to that of the recipient, so that antibodies in the plasma of the recipient do not attack the donor blood. For example: someone with blood group A red cells has anti-B in their plasma and must receive only group A or O red cells.
RhD System - RhD antigens on RBCs are also very immunogenic. While most people carry RhD antigens on their RBCs (i.e., RhD positive), ~15% of people in the UK do not have this antigen and are termed RhD negative. RhD positive patients can receive any RhD blood, but RhD negative patients will make antibodies if given RhD positive blood, which may cause haemolysis or haemolytic disease.
