Ten minutes after transfusion of group A packed red cells into a group O recipient, the patient develops fever, flank pain and dark urine. The haemolysis occurring in this reaction is mediated primarily by which mechanism?

• A IgE antibody binding to mast cells on the red cell surface
• B Cytotoxic T lymphocytes recognising foreign HLA class I antigens
• C Preformed IgM antibodies activating the classical complement pathway to completion ✓
• D IgG antibodies coating red cells for splenic macrophage clearance

Explanation

ABO-incompatible transfusion triggers a type II hypersensitivity reaction. Naturally occurring anti-A IgM binds recipient-incompatible red cells, fixes complement through the classical pathway all the way to the membrane attack complex, and lyses the cells intravascularly, releasing free haemoglobin that causes haemoglobinuria and acute renal injury. IgG-mediated extravascular clearance by splenic macrophages is the mechanism of delayed haemolytic transfusion reactions, not this acute event.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.