Blood Banking · 3 min read
Rh Blood Group System · Other Blood Group Systems
The Rh system is the second most important blood group system clinically. It contains over 50 antigens, with D, C, c, E, and e being the most significant. The D antigen is the most immunogenic non-ABO antigen.
Rh antigens are proteins encoded by the RHD and RHCE genes located on chromosome 1. The RHD gene encodes the D antigen. The RHCE gene encodes the C/c and E/e antigens. These genes are inherited as haplotypes.
Individuals who express the D antigen are Rh-positive; those lacking D are Rh-negative. Approximately 85% of Caucasians are Rh-positive. The D-negative phenotype most commonly results from deletion of the RHD gene.
Weak D phenotypes show reduced D antigen expression. Historically called Du, weak D results from mutations that cause quantitative reduction in D protein. Most weak D types are not at risk for anti-D formation and can receive D-positive blood. Partial D phenotypes have qualitative alterations in the D protein with missing epitopes. Individuals with partial D can make anti-D against epitopes they lack.
Rh antibodies are immune, resulting from transfusion or pregnancy. They are IgG, react at 37°C, and do not fix complement. Rh antibodies can cause hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. Anti-D is the most common Rh antibody, followed by anti-E, anti-c, anti-C, and anti-e.
The Kell system contains highly immunogenic antigens. K (Kell) and k (cellano) are antithetical antigens; k is high frequency. Anti-K is the most common Kell antibody and is clinically significant. The Kell antigens are destroyed by treatment with sulfhydryl reagents like DTT or AET.
The Duffy system includes Fya and Fyb antigens. The Fy(a-b-) phenotype is common in Black populations and confers resistance to Plasmodium vivax malaria. Anti-Fya and anti-Fyb are clinically significant IgG antibodies.
The Kidd system contains Jka and Jkb antigens. Kidd antibodies are notorious for causing delayed hemolytic transfusion reactions because they rapidly fall below detectable levels. Jk(a-b-) individuals resist lysis in 2M urea.
The MNS system is complex with over 40 antigens. M and N antibodies are usually IgM and clinically insignificant. Anti-S, anti-s, and anti-U are IgG and clinically significant.
The Lutheran system contains Lua and Lub antigens. Lutheran antigens show variable expression and mixed-field agglutination. The Lewis system includes Lea and Leb antigens, which are not intrinsic red cell antigens but adsorbed from plasma. Lewis antibodies are usually IgM and clinically insignificant.
The P1PK and Globoside systems include P1, P, and Pk antigens. Anti-P1 is common but usually clinically insignificant. Anti-PP1Pk (anti-Tja) is a rare, potent hemolytic antibody in p phenotype individuals.
The I and i antigens are related to ABO biochemistry. I antigen is expressed on adult red cells; i antigen predominates on cord cells. Anti-I is a common cold autoantibody associated with Mycoplasma pneumoniae infections.
Finished reading?
Lock it in with a quick Blood Banking quiz.