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Bariatric surgery deficiency — USMLE Step 3 MCQ

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ModerateSurgery (post-operative, follow-up)Bariatric surgery deficiencyUSMLE Step 3

A 42-year-old woman had Roux-en-Y gastric bypass 2 years ago and now has numbness in her feet and gait imbalance. Hemoglobin is 10.5 g/dL and mean corpuscular volume is 111 fL. Methylmalonic acid is elevated. Which of the following is the most likely explanation for this patient's findings?

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Correct answer: A — Vitamin B12 malabsorption after bypass

Roux-en-Y gastric bypass can impair vitamin B12 absorption and cause macrocytosis with neurologic symptoms.

Reference: ASMBS Nutritional Guidelines for Bariatric Surgery