A patient develops fever, rigors, hemoglobinuria (dark urine), and acute hemolytic anemia after receiving a transfusion. The most likely cause is:

• A Intravascular hemolysis from ABO-incompatible RBCs triggering complement activation ✓
• B Extravascular hemolysis from IgG-coated RBCs cleared in the spleen
• C Delayed hemolytic transfusion reaction due to alloantibody anamnestic response
• D Transfusion-related acute lung injury (TRALI) from donor antibodies

Explanation

Acute intravascular hemolysis with hemoglobinuria and hemoglobinemia is the hallmark of ABO-incompatible transfusion reactions. ABO antibodies (IgM) fix complement efficiently through the classical pathway, leading to membrane attack complex formation and intravascular lysis within minutes to hours. This is the most serious, potentially fatal transfusion reaction. IgG-mediated reactions cause extravascular hemolysis without hemoglobinuria. TRALI presents with pulmonary edema.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.