ABO



 
  • A number of different antigens are found on the human RBC, each representing a particular blood group. The most clinically important of these is the ABO blood group.
  • At a molecular level, ABO blood grouping is determined based on the presence or absence of particular sugar molecules attached to the common H antigen, found on the surface of RBCs.
  • The A and B genes code for specific glycosyltransferases that add N-acetylgalactosamine and galactose, respectively, to the H antigen. The O gene is silent and does not encode an enzyme, thus leaving the H antigen unaltered.
  • The genes that encode for the group A and group B glysosyltransferases are both individually dominant over the silent O gene. When expressed together however, the group A and group B genes are co-dominant, meaning the individual in question has the mixed phenotype, AB.
ABO blood groups at a molecular level    

  • The ABO blood system is the only blood group system in which individuals possess reciprocal, naturally occurring antibodies without prior exposure to the antigen they react with. These antibodies are directed against those antigens not expressed on the individual’s own RBCs. The antibodies are mostly of the IgM isotype and can activate complement and cause serious complications, like acute intravascular hemolysis, if ABO mismatched blood is transfused.
  • Note: The universal recipient of RBCs is AB type blood. The universal donor of RBCs is O type blood.

+ refers to a positive test based on presence of agglutination
« Previous | Next »