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Community-Acquired Pneumonia — ABIM Board MCQ

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EasyInfectious DiseasesCommunity-Acquired PneumoniaABIM Board

A 63-year-old man with suspected community-acquired pneumonia (CAP) is asking whether he should start antibiotics based on a procalcitonin (PCT) level of 0.08 ng/mL. He has clinical findings consistent with pneumonia and a radiograph showing a new infiltrate. Which statement best reflects current US clinical practice guidelines?

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Correct answer: A — Procalcitonin level alone should not determine whether to initiate antibiotic therapy

The ATS/IDSA guideline gives a strong recommendation that antibiotic initiation in CAP depends on clinical suspicion and radiographic confirmation, not procalcitonin level (Answer: A). Low PCT levels (<0.1 ng/mL) do not prevent bacterial pneumonia and do not indicate withholding antibiotics (eliminating B and C). Option D is false because PCT has never replaced clinical assessment or imaging. Option E incorrectly identifies PCT as the primary determinant of site of care; severity scores such as PSI or CURB-65 fulfill that role. This item tests whether trainees understand that PCT is a supportive stewardship tool for de-escalation, not an initiation marker.

Reference: American Thoracic Society and Infectious Diseases Society of America. Diagnosis and Treatment of Adults with Community-Acquired Pneumonia. 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6812437/