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Carbon monoxide poisoning — USMLE Step 3 MCQ

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ModerateEmergency MedicineCarbon monoxide poisoningUSMLE Step 3

A 34-year-old man and his child develop headache, dizziness, and nausea while using a generator in a garage. Pulse oximetry reads 99%, but co-oximetry shows elevated carboxyhemoglobin. Which of the following is the most likely diagnosis?

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Correct answer: E — Carbon monoxide poisoning

Multiple exposed persons with headache and elevated carboxyhemoglobin indicate carbon monoxide poisoning; pulse oximetry can be misleading.

Reference: CDC carbon monoxide clinical guidance