A patient develops rigors, hypotension, and haemoglobinuria 30 minutes after starting a blood transfusion. The Coombs test is positive. This is an acute haemolytic transfusion reaction due to which type of hypersensitivity and which immunoglobulin class?

• A Type III hypersensitivity; IgG immune complexes depositing in renal glomeruli
• B Type I hypersensitivity; IgE against donor plasma proteins
• C Type IV hypersensitivity; sensitised CD8+ T cells lysing donor RBCs
• D Type II hypersensitivity; IgM (or IgG) anti-A or anti-B antibodies activating complement ✓

Explanation

Acute haemolytic transfusion reactions (AHTR) result from ABO incompatibility: recipient's preformed IgM (anti-A or anti-B) antibodies bind donor RBC antigens, activating the classical complement pathway and causing intravascular haemolysis (haemoglobinuria). This is a Type II (cytotoxic) hypersensitivity reaction. Type I/IgE mediates allergic transfusion reactions; Type IV is delayed T-cell mediated.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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