A 41-year-old female is hospitalized for symptomatic anemia following a gastrointestinal bleed. Fifteen minutes into a transfusion of packed red blood cells, she acutely develops chills, severe lower back pain, and dark urine. Her temperature is 39.2°C (102.6°F), blood pressure is 88/50 mmHg, and heart rate is 122/min. The transfusion is immediately stopped. Which of the following best describes the predominant immunologic mechanism responsible for this patient's acute presentation?
- ACross-linking of IgE on mast cells leading to systemic histamine release
- BDeposition of circulating antigen-antibody complexes in the renal glomeruli
- Complement-mediated lysis of donor erythrocytes by preformed recipient antibodiesAnswer
- DActivation of donor cytotoxic T lymphocytes against recipient tissues
- EBinding of donor antibodies to recipient human leukocyte antigens on neutrophils
Answer
Complement-mediated lysis of donor erythrocytes by preformed recipient antibodies
The patient is experiencing an acute hemolytic transfusion reaction (AHTR), characterized by fever, hypotension, flank pain, and hemoglobinuria (dark urine) shortly after starting a blood transfusion. This is a classic Type II hypersensitivity reaction. It is caused by preformed recipient antibodies (usually anti-A or anti-B IgM) binding to donor erythrocyte antigens. This binding aggressively activates the classical complement pathway, resulting in the formation of the membrane attack complex and widespread intravascular hemolysis.
Step-by-Step Solution
Key Concept
Acute hemolytic transfusion reactions are Type II hypersensitivity responses where preformed recipient antibodies bind to donor erythrocyte antigens, triggering classical complement activation and rapid intravascular hemolysis.