Background. The heterogeneity of A and B alleles results in weak variants of these antigens. Subgroups of A differ from each other quantitatively and qualitatively. The expected frequencies of A1 and A2 subtypes will be in Hardy-Weinberg equilibrium for the Mendelian inheritance of the allelic A1 and A2 genes. The frequency of A subgroups in the population from south India is not known. The aim of our study was to study the frequency of A subtypes and the prevalence of anti-A1 antibody among this population.
Methods. Over a period of 3 years, patients' blood group was typed using a standard tube technique. Anti-A1 lectin studies were done for all patients with groups A and AB. Based on serological reactivity the samples were classified into A1/A1B, A2/A2B and weak A subgroups. The prevalence of A subgroups was determined. The significance of differences in proportions was analysed using the chi-square test.
Results. A total of 40,113 patients’ samples were typed for ABO, Rh group and A subgroups in our blood bank attached to a tertiary care hospital. Among 10,325 group A samples, 98.14% classified as A1, 1.07% as A2, and 0.01% as weak A; the remaining group A samples were neonates and reacted poorly with anti A1-lectin. The majority of AB samples (n=2,667) were of A1B type (89.28%). However, the proportion of A2B (8.99%) among AB samples was significantly higher than that of A2 in group A samples (p < 0.0001). The prevalence of anti-A1 antibodies
among A2 and A2B samples was 1.8% and 3.75%, respectively, and none of them showed reactivity at 37°C.
Conclusion. The results of our study show a significantly higher proportion of A2B subtypes than A2 subgroups. A similar imbalance is seen in blacks and Japanese. The incidence of anti-A1 antibodies is also higher among A2B patients.
Key Words: subgroups, anti-A1 lectin, A2, A2B.