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Chapter 107. Transfusion Biology and Therapy (Part 2)

Rh System The Rh system is the second most important blood group system in pretransfusion testing. The Rh antigens are found on a 30- to 32-kDa RBC membrane protein that has no defined function. Although 40 different antigens in the Rh system have been described, five determinants account for the vast majority of phenotypes. The presence of the D antigen confers Rh "positivity," while persons who lack the D antigen are Rh negative. Two allelic antigen pairs, E/e and C/c, are also found on the Rh protein. The three Rh genes, E/e, D, and C/c, are arranged in tandem. | Chapter 107. Transfusion Biology and Therapy Part 2 Rh System The Rh system is the second most important blood group system in pretransfusion testing. The Rh antigens are found on a 30- to 32-kDa RBC membrane protein that has no defined function. Although 40 different antigens in the Rh system have been described five determinants account for the vast majority of phenotypes. The presence of the D antigen confers Rh positivity while persons who lack the D antigen are Rh negative. Two allelic antigen pairs E e and C c are also found on the Rh protein. The three Rh genes E e D and C c are arranged in tandem on chromosome 1 and inherited as a haplotype i.e. cDE or Cde. Two haplotypes can result in the phenotypic expression of two to five Rh antigens. The D antigen is a potent alloantigen. About 15 of individuals lack this antigen. Exposure of these Rh-negative people to even small amounts of Rh-positive cells by either transfusion or pregnancy can result in the production of anti-D alloantibody. Other Blood Group Systems and Alloantibodies More than 100 blood group systems are recognized composed of more than 500 antigens. The presence or absence of certain antigens has been associated with various diseases and anomalies antigens also act as receptors for infectious agents. Alloantibodies of importance in routine clinical practice are listed in Table 107-1. Table 107-1 RBC Blood Group Systems and Alloantigens Blood Group System Antigen Alloantibody Clinical Significance Rh D RBC protein IgG HTR HDN C c E e Lewis Lea Leb Oligosaccharide IgM IgG Rare HTR Kell K k RBC protein IgG HTR HDN Duffy Fya Fyb RBC protein IgG HTR HDN Kidd Jka Jkb RBC protein IgG HTR often delayed HDN mild I i Carbohydrate IgM None MNSsU RBC protein IgM IgG Anti-M rare HDN anti-S -s and -U HDN .