A 32-year-old woman presents with jaundice, splenomegaly, and hemoglobin 7.5 g/dL. Peripheral smear shows numerous spherocytes and polychromasia. Direct antiglobulin (Coombs) test is strongly positive with IgG and C3 on red cells. The hemolysis in this condition occurs predominantly by which route?

• A Complement-mediated intravascular lysis by membrane attack complex
• B Mechanical fragmentation across abnormal cardiac valves
• C Extravascular phagocytosis by splenic macrophages recognizing Fc portions ✓
• D Osmotic lysis within the renal medulla

Explanation

Warm autoimmune hemolytic anemia is caused by IgG antibodies reactive at body temperature. IgG-coated red cells are recognized by Fc receptors on splenic macrophages, which partially ingest the membrane, converting cells to spherocytes that are destroyed extravascularly in the spleen. Complement fixation is incomplete with IgG, so intravascular lysis is minimal, unlike cold agglutinin disease where IgM fixes complement efficiently.

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.