What Are Blood Groups

Blood groups are complex chemical systems found on the surface of blood cells. The two main blood group systems in transfusion practice are the ABO system and the Rh(D) type. Identification of the correct blood group is important to prevent reaction following transfusion..
Blood groups are determined by a protein (antigen) on the surface of the red cell. So, the ABO system has A and B antigens and the RhD system has the D antigen.
In all, there are 30 major blood group systems. This means a person may be A RhD positive, and at the same time Kell (Kell system) positive, M and N (MNS system) positive and Lea and Leb (Lewis system) positive.

The ABO Blood Group System