Blood groups

Blood group systems are necessary to identify suitable products for transfusion.

Their clinical importance also relates to the production of alloantibodies that destroy transfused blood cells or that cross the placenta and give rise to haemolytic disease in the fetus and newborn.

This is dependent upon:

  • the frequency with which alloantigens and alloantibodies occur, which may be different among ethnic groups 
  • the functional characteristics of alloantibodies: thermal range, immunoglobulin class, titre, avidity and ability to fix complement, and 
  • the presence of autoantibodies that are relevant to the diagnosis and management of autoimmune blood disorders and that may interfere with compatibility testing

More about blood groups


ABO is the most important of all the blood group systems. There are four different ABO blood groups, determined by whether an individual's red cells carry the A antigen, the B antigen, both A and B antigens, or neither antigens.

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There are 55 antigens described in the Rh system, and new antigens continue to be discovered.

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Blood group phentoypes

An individual’s phenotype is determined by the expression of antigens on their red cells. The frequency of blood group phenotypes within a population is determined by the ethnic diversity of a region due to the patterns of inheritance of the blood groups.

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