Rh system

The Rh blood group system is the most polymorphic of the human blood groups, consisting of at least 45 independent antigens and, next to ABO, is the most clinically significant in transfusion medicine. Alloantibodies that recognize Rh antigens are usually IgG and react by the indirect antiglobulin test. Alloantibodies in the Rh blood group system can cause destruction of transfused RBCs and of fetal RBCs in hemolytic disease of the fetus and newborn (HDFN).