ABO blood grouping is critically linked to several important determinants, which are considered precursors to the formation of detectable, testable antigen. The main precursor is the H antigen. Creation of specific A and B antigens is determined by the addition of specific glycosyltransferases (enzymes) that add specific sugars to the H antigen.
These added sugars result in the precursor conversion to a detectable RBC antigen.
H Gene (Hh or HH)
The antigenic precursor on which A and B antigens are made. Without the H antigen, individuals cannot demonstrate the expression of A or B antigenic determinants on the RBC membrane surface.
|Gene||Glycosyltransferase||Immunodominant Sugar||Resulting Antigen |
| H||α-2-L-fucosyltransferase|| L-fucose || H|
| A||α-3-N-acetylgalactosaminyltransferase||N-acetyl-D-galactosamine|| A|
| B||α-3-D-galactosyltransferase|| D-galactose ||B |