Serological evaluation and differentiation of subgroups of “A” and “AB” in healthy blood donor population in Eastern India

Abstract

Background and Objectives: Weak subgroups of A antigen in A or AB blood group can be differentiated by various immunohematological investigations. These weak phenotypes mainly result from weaker expression of an alternate weak allele present at the ABO loci. Weak subgroups of A antigen either reacts weakly with anti-A antisera such as A3, Ax, and Aendor do not react at all such as Am, Ay, and Ael. In this study, we characterized and differentiated the broad and weak subgroups of A in ABO blood group system through various immunohematological investigations. Methods: The prospective study included 67,954 healthy blood donors. Initial blood grouping and antibody screening of all donor samples were performed using an automated solid-phase assay. Samples showing blood group discrepancy or weaker agglutination were subjected to battery of serological investigation including saliva hemagglutination inhibition test and adsorption-elution procedures. Results: Among 16,034 A group donors, A1were 13,276 (82.8%), A22750 (17.15%), and weak subgroups were 8 (0.05%). Among AB group, A1B donors were 5621 (84.93%), A2B 996 (15.05%), and weak subgroups of AB were 1 (0.015%). The unexpected naturally occurring anti-A1antibodies (1.9%) were of IgM type optimally reactive at 4°C with titer ranging from 1 to 8. Red cells' agglutination with anti-A and anti-AB varied from Wk + to 2+ with or without mixed field agglutination in A3, Ax, and Aendphenotypes. While saliva study revealed specific substances, adsorption-elution demonstrated “A” antigen specificity in different strengths in Am, Ay, and AmB phenotypes. Conclusion: The subgroups of A and AB are attributed to a reduced number of A antigen sites on the red cells. We conclude that differentiating weak subgroups of “A” by serological assays is possible to a great extend with technical expertise; however, molecular genotyping is essential because it confirms the result.