A 38-year-old woman with systemic lupus erythematosus presents with fatigue and jaundice. Hemoglobin is 7 g/dL, reticulocyte count 8%, LDH elevated, and peripheral smear shows numerous spherocytes. The direct antiglobulin (Coombs) test is strongly positive when performed at 37 degrees C. What is the defining feature of this hemolytic anemia?
- A IgG antibody coating red cells, causing extravascular destruction by splenic macrophages ✓
- B IgM antibody binding at 4 degrees C, causing intravascular complement lysis
- C IgG antibody directed against the P blood group antigen with biphasic lysis
- D IgA antibody causing sequestration of red cells in hepatic sinusoids
Correct answer: A. IgG antibody coating red cells, causing extravascular destruction by splenic macrophages
Explanation
Warm antibody AIHA is caused by IgG (occasionally IgA) antibodies reactive at body temperature. Opsonized cells undergo extravascular hemolysis, with partial phagocytosis by splenic macrophages producing the spherocytes seen on smear. Option B describes cold agglutinin disease, which is IgM mediated. Option C describes paroxysmal cold hemoglobinuria. Splenic sequestration by IgA in hepatic sinusoids is not a recognized mechanism of AIHA.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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