How many days after a tick bite should a Borrelia test be taken? - briefly
Serologic testing for Borrelia is recommended no sooner than 14 days after a tick attachment, with optimal sensitivity from 21 to 28 days post‑bite. Testing earlier may yield false‑negative results, while later testing remains appropriate for confirming infection.
How many days after a tick bite should a Borrelia test be taken? - in detail
The interval between a tick attachment and a reliable Borrelia assay depends on the kinetics of the immune response and the diagnostic method employed.
Serologic tests (ELISA followed by Western blot) detect IgM and IgG antibodies that typically become measurable 2 – 4 weeks after inoculation. Testing before this window yields a high false‑negative rate because antibody concentrations remain below detection thresholds.
Molecular techniques (PCR) can identify Borrelia DNA within days of the bite, especially from skin biopsies of erythema migrans lesions. Sensitivity of blood PCR is low during early infection, limiting its utility as a sole screening tool.
Practical recommendations:
- Initial serology at 21–28 days post‑exposure.
- If the first result is negative and clinical suspicion persists, repeat testing at 45–56 days.
- PCR may be added when a rash is present within the first week, provided a specimen can be obtained.
Factors influencing timing include:
- Type of assay (ELISA, immunoblot, PCR).
- Presence and onset of characteristic skin lesions.
- Patient’s immune status, which can delay antibody production.
Adhering to the 3‑ to 4‑week window for the first serologic evaluation maximizes diagnostic yield while allowing for early molecular confirmation when appropriate.