A 35-year-old woman with a history of gastric bypass surgery presents with fatigue and glossitis. Labs show Hb 7.8 g/dL, MCV 112 fL, LDH 1200 U/L, indirect bilirubin 3.2 mg/dL, haptoglobin <10 mg/dL. Which mechanism explains the elevated LDH and indirect bilirubin?

• A Autoimmune hemolysis
• B Ineffective erythropoiesis with intramedullary hemolysis ✓
• C Mechanical hemolysis from prosthetic valve
• D Oxidative hemolysis

Explanation

In megaloblastic anemia from A12 deficiency (after gastric bypass), there is ineffective erythropoiesis with destruction of RBC precursors within the bone marrow (intramedullary hemolysis). This releases LDH and unconjugated bilirubin into circulation without peripheral hemolysis markers like schistocytes. The macrocytosis, glossitis, and post-surgical context point to A12 deficiency.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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