A 64-year-old man is admitted to the hospital for management of a bleeding duodenal ulcer. His hemoglobin concentration is 6.5 g/dL, and he is started on a packed red blood cell transfusion. Fifteen minutes after the transfusion begins, he develops fever, chills, and severe lower back pain. His blood pressure decreases from 128/78 mm Hg to 92/58 mm Hg, and his urine becomes dark brown. The transfusion is immediately stopped. Laboratory studies obtained several hours later show an elevated lactate dehydrogenase level, decreased haptoglobin concentration, and indirect hyperbilirubinemia.
Which of the following is the most likely mechanism responsible for this patient's condition?
The correct answer is:
D) Recipient antibodies binding donor erythrocytes and activating complement.
This patient has an acute hemolytic transfusion reaction, a life-threatening complication that typically occurs within minutes to hours of transfusion. The classic presentation includes fever, chills, hypotension, flank or back pain, hemoglobinuria, and laboratory evidence of intravascular hemolysis. The most common cause is ABO incompatibility due to a clerical or blood-matching error. Preformed recipient IgM antibodies bind donor red blood cell antigens, activating the complement cascade and causing rapid intravascular hemolysis. Released hemoglobin can precipitate in the kidneys, leading to acute kidney injury.
Answer choice A: Anti-IgA antibodies reacting against donor plasma proteins, is incorrect. This describes an anaphylactic transfusion reaction, which occurs most commonly in IgA-deficient recipients. Patients typically develop hypotension, wheezing, urticaria, and respiratory distress rather than hemoglobinuria and laboratory evidence of hemolysis.
Answer choice B: Donor lymphocytes attacking recipient tissues, is incorrect. This describes transfusion-associated graft-versus-host disease. Symptoms typically develop days to weeks after transfusion and include rash, diarrhea, hepatitis, and pancytopenia.
Answer choice C: IgE-mediated mast cell degranulation in response to donor proteins, is incorrect. This mechanism causes an allergic transfusion reaction characterized by pruritus, urticaria, and flushing. Hemolysis does not occur.
Answer choice E: Recipient sensitization to donor leukocyte antigens, is incorrect. This mechanism causes a febrile nonhemolytic transfusion reaction. Patients develop fever and chills during transfusion, but there is no intravascular hemolysis, hemoglobinuria, or severe hypotension.
Key Learning Point
Acute hemolytic transfusion reactions occur when preformed recipient antibodies, usually IgM directed against ABO blood group antigens, bind donor erythrocytes and activate complement. This causes intravascular hemolysis, leading to fever, chills, hypotension, flank or back pain, hemoglobinuria, elevated LDH, decreased haptoglobin, and indirect hyperbilirubinemia. Immediate cessation of the transfusion is required.
