Hives and rash usually indicate an allergic reaction. Hematuria is due to a variety of causes. Fever and chills usually indicate a febrile reaction. Positive DAT due to conditions other than sensitization to red cell alloantigens is not uncommon. Therefore a positive DAT in the posttransfusion specimen with a negative DAT in the pretransfusion specimen is more likely to indicate alloimmunization.

The most definite indication that a patient has been sensitized to a specific red cell antigen is: