The International Society of Blood Transfusion
currently recognizes 30 blood-group systems (including the ABO
and Rh systems). Thus, in addition to the ABO antigens and Rh antigens, many other antigens are expressed on the RBC surface membrane. For example, an individual can be AB, D positive, and at the same time M and N positive (MNS system), K positive (Kell system), Lea or Leb negative (Lewis system), and so on, being positive or negative for each blood group
system antigen. Many of the blood group systems were named after the patients in whom the corresponding antibodies
were initially encountered.