A 35-year-old woman presents with fatigue, jaundice, and splenomegaly. Smear shows spherocytes, reticulocyte count 8%, and the direct antiglobulin (Coombs) test is strongly positive with IgG and C3 on red cells. Autoantibodies react best at 37 degrees C. The hemolysis is mediated mainly by:

• A Complement-mediated intravascular lysis by IgM
• B Osmotic swelling of complement-deficient red cells in the renal medulla
• C Microvascular fibrin strand shearing of red cells
• D Splenic macrophage phagocytosis of IgG-coated cells (extravascular) ✓

Explanation

Warm autoimmune hemolytic anemia is caused by IgG antibodies optimal at body temperature. IgG-coated cells are recognized by Fc receptors on splenic macrophages, which remove membrane and convert cells to spherocytes, causing predominantly extravascular hemolysis. Complement-mediated intravascular lysis by IgM defines cold agglutinin disease, fibrin shearing defines microangiopathic hemolytic anemia, and option B describes no recognized mechanism. The positive Coombs test with IgG confirms the immune etiology.

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.