Microbial diagnostics · USMLE Step 1

A patient presents with urethritis likely caused by Chlamydia trachomatis. Which test is the diagnostic method of choice?

  1. Serology for IgM antibodies
  2. NAAT of urine or swab
  3. Gram stain of urethral discharge
  4. Culture on blood agar
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Correct answer: NAAT of urine or swab

NAAT is highly sensitive for C. trachomatis and is the preferred diagnostic test. Chlamydia does not appear on Gram stain.

Difficulty: Medium Question 15 of 20

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