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There are many blood groups in the human population including ABO, Rh, Kidd, Kell, Duffy, MNS and Lewis. The most important of these are ABO and RhD. Transfusion with ABO incompatible blood can lead to severe and potentially fatal transfusion reactions. RhD is highly immunogenic and can lead to red cell haemolysis in certain settings.
ABO antigens and antibodies
The ABO blood group is the most important of all the blood group systems. There are four different ABO blood groups determined by whether or not an individual's red cells carry the A antigen, the B antigen, both A and B antigens or neither. Normal healthy individuals, from early in childhood, make red cell antibodies against A or B antigens that are not expressed on their own cells. These naturally occurring antibodies are mainly IgM immunoglobulins. They attack and rapidly destroy red cells carrying the corresponding antigen. For example, anti-A attacks red cells of Group A or AB. Anti-B attacks red cells of Group B or AB.
Name of Blood Group Antigens present on
the red cell surface ABO antibodies present in the plasma
Type O nil anti-A and anti-B
Type A A antigen anti-B
Type B B antigen anti-A
Type AB A and B antigens nil
If ABO incompatible red cells are transfused, red cell haemolysis can occur. For example if group A red cells are infused into a recipient who is group O, the recipient's anti-A antibodies bind to the transfused cells. An ABO incompatible transfusion reaction may result in overwhelming haemostatic and complement activation, resulting in shock, renal failure & death.
Rhesus D (RhD) antigen
There are more than 40 different kinds of Rh antigens. The most significant Rh antigen is RhD. When RhD is present on the red cell surface, the red cells are called RhD positive. Approximately 80% of the Australian population are RhD positive. The remaining 20% of the population that lack the RhD antigen are called RhD negative. Antibodies to RhD develop only after an individual is exposed to RhD antigens via transfusion, pregnancy or organ transplantation. Anti RhD (or anti-D) antibodies destroy RhD positive red cells and can lead to haemolysis.