A 42-year-old woman is admitted to the hospital for elective surgery. She receives a packed red blood cell (PRBC) transfusion intraoperatively. Within minutes of the transfusion, she develops fever, chills, hypotension, tachycardia, and hemoglobinuria (dark urine). The transfusion is immediately stopped. Laboratory testing reveals hemolysis, and a direct antiglobulin test (Coombs test) is positive. Question: What is the most likely cause of this patient’s transfusion reaction?
