Microbial diagnostics · USMLE Step 1

A throat swab from a patient with suspected streptococcal pharyngitis undergoes rapid antigen detection testing. What is a key limitation of this test?

  1. High rate of false negatives
  2. High rate of false positives
  3. Cannot detect Group A Streptococcus
  4. Requires 48 hours for results
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Correct answer: High rate of false negatives

Rapid antigen tests for Group A Streptococcus have reduced sensitivity. Negative results often require confirmation with culture.

Difficulty: Medium Question 2 of 20

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