Serological and secretor status analysis of A_m phenotypes: Two cases from Northeast India

In ABO blood grouping, a type II discrepancy refers to weak or absent antigen reactions in cell grouping, often indicating a weak ABO subgroup. The Am phenotype is a rare weak A subgroup variant, distinguished by absent agglutination with anti-A antisera and normal A substance in saliva. Reporting such rare phenotype is vital to improve awareness and diagnostic accuracy, especially in Northeast region of India, where access to advanced serological tools is limited.

During routine blood grouping, type II ABO discrepancies were noted in two cases. Comprehensive immunohematological workup, including cell grouping by conventional tube technique using different lectins and at varying temperatures, adsorption-elution studies, and secretor testing, was performed. Adsorption-elution studies confirmed weak A antigen expression. Secretor testing demonstrated the presence of A and H substances in saliva, consistent with Am phenotype.

Our cases highlight the diagnostic complexity of weak A subgroups. In resource-limited settings, with limited access to molecular diagnostics, detailed serological testing remains critical for ABO subgroup identification. Proper recognition of such phenotypes ensures transfusion safety and prevents misclassification.