GERD and Peptic Ulcer Disease USMLE Step 1 Practice Question
A 48-year-old man on chronic omeprazole therapy for GERD presents with fatigue and paresthesias. Vital signs show BP 128/76 mmHg, HR 82 bpm, RR 16, temp 37°C, SpO2 98%. Laboratory evaluation reveals B12 level of 180 pg/mL (normal 200–900), elevated methylmalonic acid, normal folate, and normal hemoglobin. Upper endoscopy shows no active ulceration. Which of the following is the most likely mechanism of this finding?
Answer choices
- ABacterial overgrowth consuming dietary B12
- BReduced dietary vitamin B12 intake
- CDecreased intrinsic factor production by parietal cells due to acid suppressionCorrect answer
- DOmeprazole-induced autoimmune gastritis
- EDirect inhibition of cobalamin absorption in the terminal ileum
- FImpaired conversion of cobalamin to its active metabolic forms by hepatic methylation reactions
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