Rh Blood Group System

        The Rh (not Rhesus) system is the second most important blood group system in transfusion medicine because antigen-positive RBCs frequently immunize antigen-negative individuals through transfusion and pregnancy.

       Inheritance of Rh antigens is determined by a complex of two closely linked genes: one encodes the protein carrying D antigen (RhD); the other encodes the protein carrying C or c and E or e antigens (RhCE). RBCs from Rh-positive people have both RhD and RhCE, whereas Rh-negative RBCs have only RHCE. In the Rh system, eight common antigen combinations or haplotypes are possible: Dce (R₀, Rh₀), DCe (R₁, Rh₁), DcE (R_2, Rh₂), DCE (R_Z, Rh_z), ce (r, rh), Ce (r', hr'), cE (r″, hr″), and CE (ry, rh″). The letter "d" is commonly used to designate the lack of D, but there is no d antigen or anti-d.