The Frequency and Nature of Blood Group A₃

Abstract

A special survey of 20,826 random blood donor specimens collected in Ontario, Canada yielded one A 3 blood while a review of blood grouping worksheets of 158,000 individuals in this area also yielded one A 3 blood. These frequencies are much lower than the frequency found in Denmark around 1940 by Gammelgaard, 44 per 10 5 , perhaps due to the present availability of high titer immune anti‐A. Elution studies on these two A 3 bloods show that both the agglutination‐positive and the agglutination‐negative cells absorb anti‐A, indicating that A 3 is not always an A 2 + O mixture as has been suggested. Fluorescent antibody studies revealed a marked cell‐to‐cell variability in fluorescence and, therefore, presumably, cell A antigen content. This finding confirms Gammelgaard's earlier report. This variability, together with a threshold value of A antigen required for agglutination, could explain the characteristic appearance of A 3 : agglutinates and free cells.