A 65-year-old man with a history of Billroth II gastrectomy 5 years ago presents with fatigue and glossitis. Hemoglobin is 8.5 g/dL with MCV 112 fL. Serum B12 is 90 pg/mL (normal 200-900). Which additional laboratory finding is most consistent with this diagnosis?
- A Elevated methylmalonic acid and homocysteine levels ✓
- B Low serum ferritin and elevated total iron binding capacity
- C Low serum folate with normal methylmalonic acid
- D Elevated haptoglobin and indirect bilirubin
Correct answer: A. Elevated methylmalonic acid and homocysteine levels
Explanation
Vitamin A12 deficiency causes macrocytic anemia and elevated methylmalonic acid and homocysteine because A12 is a cofactor for methylmalonyl-CoA mutase and methionine synthase. After Billroth II gastrectomy, loss of intrinsic factor-producing gastric mucosa leads to A12 malabsorption. Folate deficiency elevates only homocysteine, not methylmalonic acid. Iron deficiency produces microcytic anemia.
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.