OBJECTIVES: Low titer O METHODS: This was a retrospective review of consecutive trauma patients who received prehospital LTO+WB over a 4.5-year period. We used EMS agency transfusion records and institutional blood bank data from two urban level I trauma centers for records on blood transfusion reactions. Excluded from the study were patients declared dead on arrival to the hospital, patients transfused for non-traumatic complaints, patients for whom hospital records were unavailable, and any transfusion reaction that occurred more than 10 days after the prehospital transfusion. Descriptive statistics were used for data analysis. RESULTS: Of 1126 prehospital transfusions 572 met inclusion criteria. There were 2 (0.35%) suspected transfusion reactions, none of which were determined to be hemolytic reactions. There was 1 febrile non-hemolytic reaction on hospital day 1 and there was 1 allergic reaction with hives and shortness of breath that occurred on hospital day 1. CONCLUSIONS: Prehospital LTO+WB is safe to use and has a similar rate of transfusion reaction as when given in-hospital. Concerns about transfusion reactions caused by LTO+WB should not preclude its use prehospital. Regardless of the low incidence of transfusion reactions, prehospital personnel should be trained in their recognition and management. Limitations include retrospective study design and the inability to distinguish transfusion reactions from prehospital LTO+WB versus reaction to blood products transfused at the trauma center.