Rh blood group system
The Rh blood group system is a human blood group system. It contains proteins on the surface of red blood cells. After the ABO blood group system, it is the most likely to be involved in transfusion reactions. The Rh blood group system consisted of 49 defined blood group antigens in 2005. As of 2023, there are over 50 antigens among which the five antigens D, C, c, E, and e are the most important. There is no d antigen. Rh(D) status of an individual is normally described with a positive (+) or negative (−) suffix after the ABO type (e.g., someone who is A+ has the A antigen and Rh(D) antigen, whereas someone who is A− has the A antigen but lacks the Rh(D) antigen). The terms Rh factor, Rh positive, and Rh negative refer to the Rh(D) antigen only. Antibodies to Rh antigens can be involved in hemolytic transfusion reactions and antibodies to the Rh(D) and Rh antigens confer significant risk of hemolytic disease of the fetus and newborn The Rh blood group system has two sets of nomenclatures: one developed by Ronald Fisher and R. R. Race, the other by . Both systems reflected alternative theories of inheritance. The Fisher–Race system, which is more commonly in use today, uses the CDE nomenclature. This system was based on the theory that a separate gene controls the product of each corresponding antigen (e.g., a "D gene" produces D antigen, and so on). However, the d gene was hypothetical, not actual. The Wiener system used the Rh–Hr nomenclature. This system was based on the theory that there was one gene at a single locus on each of the two copies of chromosome 1, each contributing to production of multiple antigens. In this theory, a gene R1 is supposed to give rise to the "blood factors" Rh0, rh′, and rh′′ (corresponding to modern nomenclature of the D, C, and E antigens) and the gene r to produce hr′ and hr′′ (corresponding to modern nomenclature of the c and e antigens). Notations of the two theories are used interchangeably in blood banking (e.g., Rho(D) meaning RhD positive).
