Overt immediate hemolytic transfusion reaction attributable to anti-Wr(a).

Wr(a) is a low-prevalence antigen. Anti-Wr(a) is a relatively common antibody present in approximately 1 in 100 healthy blood donors. Anti-Wr(a) is reported to cause different degrees of hemolysis in transfusion and in HDN, ranging from benign to severe. This report describes an acute overt hemolytic transfusion reaction in a patient whose serum contained anti-Wr(a) and who received a Wr(a+) RBC component.