The most common cause of fatal transfusion reactions is:

The most common cause of fatalities related to transfusion reactions result from ABO-incompatible transfusion related to clerical/tehcnician's error. Most such reactions occur if a type O person receives type A Red cells owing to a clerical error that occurs either at the time the blood sample was drawn, during processing in the laboratory, or at the time a unit is administered. The impoance of extremely careful labeling, transfer, and handling of specimens and of cross-matched blood products cannot be overemphasized. Allergic and other reactions are common but rarely fatal. The transmission of bacterial organisms (e.g., Staphylococcus aureus) has been repoed especially with platelet concentrates maintained at or near room temperature. But such reactions are rare.