Microbial diagnostics · USMLE Step 1

A patient with a bull’s-eye rash is suspected of having Lyme disease. What is the most appropriate initial diagnostic test?

  1. PCR of blood sample
  2. ELISA for Borrelia antibodies
  3. Western blot assay
  4. Blood culture on agar
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Correct answer: ELISA for Borrelia antibodies

ELISA is the first-line serologic screening test. Positive ELISA must be confirmed with Western blot.

Difficulty: Medium Question 9 of 20

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