A second example of anti-Es^a, an antibody to a high-incidence Cromer antigen

A blood sample contained an antibody to a high-incidence antigen that reacted with all red blood cells (RBCs) tested by the indirect antiglobulin test (IAT). The antibody reacted with papain-, ficin-, and trypsin-treated RBCs, but not with α-chymotrypsin-treated RBCs. This pattern of reactivity suggested the possibility that the antibody was recognizing an antigen in the Cromer blood group system. Tests against RBCs deficient in decay-accelerating factor (which carries the Cromer antigens) were weakly positive. Tests with antibodies to high-incidence Cromer antigens and with RBCs lacking high-incidence Cromer antigens led to identification of the second example of anti-Es^a in an Es(a-) person. The antibody was IgGl and reacted by the IAT to a titer of 64. The monocyte monolayer assay indicated potential clinical significance of this antibody in relation to transfusion.