“…In India there is more variation with a high frequency of Se in the North (up to 0.75) and low frequency in the South (0.22). Measurements of relative agglutinability, obtained by counting the number of cells agglutinated by anti -A in a cell counter, and site density, determined with radiolabelled rabbit IgG anti -A [223,224] , are shown in Table 2.15 . In many cases weak A subgroups have been found and associated with ABO mutations although serological analyses have been insuffi cient for categorising the phenotype, usually because of unavailability of secreted material.…”