A 45-year-old alcoholic presents with macrocytic anemia and hypersegmented neutrophils. Bone marrow biopsy shows megaloblastic changes. Serum methylmalonic acid (MMA) and homocysteine levels are both elevated. The most likely nutritional deficiency is:

• A Folate deficiency
• B Vitamin B12 (cobalamin) deficiency ✓
• C Vitamin B6 (pyridoxine) deficiency
• D Thiamine deficiency

Explanation

Elevated serum methylmalonic acid (MMA) distinguishes vitamin B12 deficiency from folate deficiency, as B12 (as adenosylcobalamin) is required for the conversion of methylmalonyl-CoA to succinyl-CoA. Both B12 and folate deficiency raise homocysteine, but only B12 deficiency raises MMA. Folate deficiency raises homocysteine without affecting MMA. This biochemical distinction is clinically important because treating B12 deficiency with folate can correct the megaloblastic anemia but worsen subacute combined degeneration.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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