A blood group system is a group of blood group antigens typically inherited from one gene (but occasionally more than one). The ISBT has identified 36 blood group systems. While most blood group systems contain antigens that have similar structural features, such is not always the case. Some systems are more important in daily practice than others, and we spend most of our time dealing with issues in those systems. Here are the most important blood group systems: ABO, Rh, Kell, Kidd, Duffy, and MNS (the other systems may also lead to problems, of course, just much less often). Those learning blood banking should focus first on mastery of those groups.

Why are these 6 systems most important, you ask? Well, the vast majority of the alloantibodies formed in response to exposure to blood group antigens in these systems may cause harm to transfusion recipients or babies born to moms carrying the alloantibodies. We call this being “clinically significant.”