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Metformin-associated vitamin B12 deficiency — USMLE Step 3 MCQ

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ModerateInternal Medicine (chronic management)Metformin-associated vitamin B12 deficiencyUSMLE Step 3

A 63-year-old woman with type 2 diabetes has progressive numbness in her feet and fatigue. She has taken metformin for 8 years. Hemoglobin is 10.8 g/dL, mean corpuscular volume is 108 fL, and A1c is 7.2%. Neurologic examination shows reduced vibration sense. Which of the following is the most likely explanation for this patient's findings?

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Correct answer: E — Reduced vitamin B12 absorption related to long-term metformin use

Long-term metformin therapy is associated with vitamin B12 deficiency, which can cause macrocytic anemia and neuropathy.

Reference: ADA Standards of Care in Diabetes