Incompatible crossmatch: First sign of a hemolytic transfusion reaction due to out-of-group platelet transfusion.

Platelet (PLT) transfusion is undertaken in a variety of clinical settings with thrombocytopenia, with or without bleeding. Since PLTs are most often stored in donor plasma, group-specific PLT transfusions are preferred to out-of-group transfusions. PLTs adsorb ABO antigens over their surface from the plasma.