Karl Landsteiner categorised blood groups into the ABO and Rh blood groups. The different ABO blood groups are referred to as blood group A, B, AB and O. The presence of the ‘Rh’ antigen in blood is called ‘Rh’ positive and the absence of the same is called ‘Rh’ negative.
Individuals with A blood group have ‘A’ antigen and anti-B antibody, B blood group have ‘B’ antigen and anti-A antibody, AB blood group have both ‘A’ and ‘B’ antigens and no antibodies, O blood group have no antigens and have both anti-A and anti-B antibodies.
During blood transfusion, specific antigens and antibodies present in the blood may react and cause the agglutination of RBCs. Hence, blood group matching is carried out before blood transfusion. This table showcases the results of ABO blood group matching between different blood groups of donors and recipients.
From the table, it is clear that individuals with blood group ‘O’ can donate blood to people of all blood groups, but receive blood only from individuals with blood group ‘O’. While individuals with blood group ‘AB’ can receive blood from all blood group types, they can donate blood only to individuals with blood group ‘AB’.
Hence, individuals with blood group ‘O’ type are called ‘universal donors’, while individuals with blood group ‘AB’ type are called ‘universal recipients’. In addition to ABO blood grouping, Rh blood group matching is also carried out during blood transfusion. This is because, if Rh positive blood is transfused to a Rh negative person, it can induce the formation of ‘Rh’ antibodies resulting in the agglutination of RBCs.
Such incompatibility takes place when an Rh negative woman carries an Rh positive foetus, leading to erythroblastosis foetalis. Erythroblastosis foetalis can be prevented by injecting anti-Rh antibodies, commercially called rhogams into the Rh negative mother, immediately after her first delivery.