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Lyme Disease Blood Tests: Timing Matters for Accuracy

Why Early Tests Can Be Negative

  • Antibody response takes 2–6 weeks to reach detectable levels.
  • Early localized disease (erythema migrans) – clinical diagnosis; treat without waiting for serology.
  • IgM peaks 3–6 weeks; IgG rises after 4–6 weeks, persists years.

Two‑Tier Testing (CDC/IDSA)

  1. Screening: ELISA or IFA for total/ IgM+IgG.
  2. Confirmatory: Western blot (IgM if ≤30 days; IgG if >30 days).

Interpretation Caveats

  • False‑negative early; false‑positive from cross‑reactivity (syphilis, EBV, autoimmune).
  • Do not test asymptomatic people.
  • PCR on skin biopsy/CSF/joint fluid for specific scenarios.

Clinical Guidance

  • EM rash + exposure history → treat empirically (doxycycline 100 mg BID × 10–14d).
  • If symptoms persist after negative early test, retest in 4–6 weeks.
  • Chronic symptoms post‑treatment: evaluate for other causes; prolonged antibiotics not recommended.

Timing and pre‑test probability are critical for Lyme serology.

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