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Vitamin B12 deficiency with metformin — ABFM Board MCQ

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ModerateEndocrine/MetabolicVitamin B12 deficiency with metforminABFM Board

A 68-year-old woman taking metformin for 12 years reports numbness in her feet and fatigue. CBC shows macrocytosis. Monofilament testing is mildly reduced. Which of the following is the most appropriate next step?

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Correct answer: B — Check vitamin B12 level

Long-term metformin can contribute to vitamin B12 deficiency, which may cause macrocytosis and neuropathy symptoms.

Reference: ADA Standards of Care in Diabetes 2026: https://professional.diabetes.org/standards-of-care