The Inb antigen of the Indian blood group system is a high-prevalence antigen. The presence of alloanti-Inb in a recipient may pose a problem in finding compatible blood for transfusion. The aim of this study was to screen blood donors for Inb 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 Inb 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 Ina, and samples typed as In(a+) were then tested both serologically and molecularly for Ina and Inb to find homozygous