Microbial diagnostics · USMLE Step 1

A patient with suspected tuberculosis undergoes initial testing. Which diagnostic method is most sensitive for detecting active TB infection?

  1. Chest radiography
  2. Sputum acid-fast smear microscopy
  3. Interferon-gamma release assay
  4. Sputum nucleic acid amplification
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Correct answer: Sputum nucleic acid amplification

NAAT detects M. tuberculosis DNA and provides rapid and sensitive results. It is more reliable than smear alone for active disease.

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