ABO blood groups consist of three main carbohydrate antigens; A, B and H antigens. The H antigen is found on all red cells with the exception of an extremely rare situation known as the ‘’Bombay Phenotype’’. The H antigen is made before either A or B antigens can be made, resulting in a reciprocal relationship between the amount of H and the amount of A and/or B on a red cell. Individuals with the A, B and AB alleles express glycosyltransferase activities that convert the H antigen to the A antigen or to the B antigen. Group A and B people therefore have less H than group O people.

The Biorex Diagnostics Anti-H blood grouping reagent is prepared from a Ulex Europaeus seed extract, diluted with a sodium chloride solution containing bovine albumin. This reagent is supplied ready for use and does not require any further dilution or addition.