Detection of a rare subgroup of A phenotype while resolving ABO discrepancy

Weaker subgroups of ABO blood group system give rise to discrepancies between forward and reverse grouping and cause diagnostic difficulties in routine blood banking. Weaker subgroups of A blood group that have been reported so far include A3, Aend, Ax, Am, Ay, and Ael. We report a case of a 54-year-old patient whose red cells showed a discrepancy between cell and serum grouping on initial testing. Serological investigation included absorption elution tests and saliva testing after performing initial blood grouping. Molecular genotyping of the ABO gene was performed by DNA sequencing of exons 6 and 7 of the ABO gene. The serological characteristics of the patient's red cells were similar to Ax subtype. The patient was a secretor and only H substance was present in the saliva. Serum did not show the presence of anti-A1. Molecular genotyping confirmed the ABO status as Aw06/O13. The weak A phenotype identified in the propositus had serological characteristics similar to Ax and showed the ABO genotype Aw06/O13. Although Aw06 allele has been previously reported in the Indian population, this is the first study to report O13 allele in the Indian population.