Evidence for Two Anomalous I Blood Group Determinants

One normal donor has been found whose red blood cells type as I positive with all anti‐I sera except those obtained from patients with chronic cold hemagglutinin disease (CCHD). In addition, these cells had more H than other random O cells and may be devoid of i antigen. Complete absorption of non‐CCHD anti‐I with the unusual cells left an anti‐I reactive with other I positive cells. These unique cells have allowed definition of at least two separate I determinants present on adult cells.