How long after a tick bite should blood be taken for Borrelia testing? - briefly
Serologic testing becomes reliable about two to three weeks after exposure, with peak sensitivity at four to six weeks. Testing sooner may produce false‑negative results.
How long after a tick bite should blood be taken for Borrelia testing? - in detail
Blood samples for detecting Borrelia burgdorferi should be drawn no earlier than three weeks after the bite. At this point most patients develop detectable antibodies; serologic tests such as ELISA become reliable. Testing before this interval yields a high false‑negative rate because the immune response has not yet matured.
If the patient presents with early localized signs (e.g., erythema migrans) and no laboratory confirmation is required for treatment, therapy may begin without testing. When laboratory confirmation is needed, a second sample collected six to eight weeks after exposure improves diagnostic accuracy, especially if the first test was negative but clinical suspicion remains.
Guidelines recommend the following schedule:
- First draw: ≥21 days post‑exposure; perform ELISA, confirm positives with Western blot.
- Second draw (if needed): 42–56 days post‑exposure; repeat serology to capture late seroconversion.
- PCR testing: Consider only on synovial fluid, cerebrospinal fluid, or skin biopsy; not useful on whole blood for routine diagnosis.
Repeat testing is justified when:
- Initial serology is negative but symptoms persist or evolve.
- The patient is immunocompromised, delaying antibody production.
- There is a need to document seroconversion for legal or occupational reasons.
Choosing the appropriate interval balances the risk of missing early infection against the cost of unnecessary testing. The three‑week minimum and the six‑to‑eight‑week follow‑up represent the consensus timing for reliable Borrelia serology.