Transfusion medicine handbook

4. Blood Components

4.1 ABO Blood Groups and Antibodies

ABO is the most important of the human blood group systems. There are four different ABO blood groups, determined by whether or not an individual's red cells carry one, both or neither of the A and B antigens (see Table 4.1 ABO Blood Groups and Antibodies).

Normal healthy individuals, from early childhood, make red cell antibodies against the A or B antigens that are not expressed on their own cells. These naturally occurring antibodies are mainly IgM immunoglobulins and can rapidly bind to and destroy red cells carrying the corresponding antigen.

If ABO incompatible red cells are transfused, intravascular haemolysis of these red cells can occur. An ABO incompatible transfusion reaction may result in overwhelming disruption of haemostatic equilibrium and complement activation, resulting in shock and renal failure. This can be fatal, even after transfusion of a small volume of incompatible blood.

Table 4.1: ABO Blood Groups and Antibodies