A unique approach to screen for blood donors lacking high-prevalence antigen In^b of the Indian blood group system

The In^b antigen of the Indian blood group system is a high-prevalence antigen. The presence of alloanti-In^b in a recipient may pose a problem in finding compatible blood for transfusion. The aim of this study was to screen blood donors for In^b and to include individuals found to be In(b–) in our rare donor registry. To save resources, a unique study design was constructed. Blood group O donors were tested for In^b because their red blood cell (RBC) units could serve recipients across all ABO groups. EDTA blood samples were used for serologic and genomic testing. These samples were first tested serologically for In^a, and samples typed as In(a+) were then tested both serologically and molecularly for In^a and In^b to find homozygous IN*01/01 [i.e., the predicted In(b–) phenotype]. A cost-conservative approach in using recycling of antibody was adopted to economize available resources. Of 6300 donors, 196 donor samples typed as In(a+) and were also found to be In(b+) when tested by serologic and genomic methods. Although none of the donors typed as In(b–), the statistical analysis suggests the expected prevalence for this rare phenotype to be 0.02 percent among the total number of donors tested. In conclusion, this report presents a unique cost-conservative approach using limited reagents to screen a large number of donors for the rare In(b–) phenotype.