The incidence of anti-Wra and Wra antigen in blood donors and hospital patients.

A retrospective study of positive 37 degrees C indirect antiglobulin test (IAT) for compatibility following negative antibody screens in a hospital laboratory revealed an unexpectedly high incidence of Wra-incompatible units. Over the course of 1 month 1112 routine patients' samples containing no other atypical antibodies were tested for the presence of anti-Wra. Anti-Wra was found in 88 patients, an incidence of 7.9%. Testing of 5098 healthy blood donor samples found 54 donors positive for anti-Wra, an incidence of 1.06%. A survey of 5253 healthy blood donor samples for Wra antigen found only two Wra-positive samples, suggesting an incidence between 1 in 1000 and < 1 in 10,000. The significance of this finding is discussed in relation to the continuing use of an IAT compatibility test.