A 22-year-old woman is found to have selective IgA deficiency (serum IgA <7 mg/dL) on routine screening before blood donation. She is asymptomatic. She later receives a blood transfusion and develops severe anaphylaxis. What is the most likely immunological mechanism?
- A Pre-existing anti-IgA antibodies of IgG or IgE class reacting with donor IgA ✓
- B IgE-mediated mast cell degranulation against red blood cell antigens
- C Immune complex deposition in pulmonary vasculature
- D Complement-mediated intravascular haemolysis
Correct answer: A. Pre-existing anti-IgA antibodies of IgG or IgE class reacting with donor IgA
Explanation
Patients with selective IgA deficiency may develop anti-IgA antibodies (IgG or IgE class) due to exposure through prior transfusions or pregnancy. When they receive blood products containing IgA, these antibodies trigger anaphylaxis. This is a well-recognised complication; IgA-deficient patients requiring transfusion should receive washed red cells or IgA-deficient blood products. Standard ABO/Rh incompatibility reactions involve complement-mediated haemolysis, not anaphylaxis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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