How long after a tick bite should blood be tested for borreliosis? - briefly
Blood testing for Lyme disease is typically performed 2–4 weeks after a tick attachment to allow seroconversion; a follow‑up test at 3 months is advised if initial results are negative and symptoms persist.
How long after a tick bite should blood be tested for borreliosis? - in detail
Blood should be drawn for serologic evaluation of Lyme disease no sooner than two weeks after the bite, because specific antibodies normally become detectable in that interval. Testing at 2–4 weeks captures the initial IgM response; a second sample collected at 6–12 weeks assesses the IgG response, which persists longer and confirms infection when the early result is negative or equivocal.
- First draw (≈14 days post‑exposure): ELISA for IgM and IgG. A positive or borderline result requires confirmation by Western blot.
- Second draw (≈45–84 days): Repeat ELISA and confirmatory Western blot if the first test was negative but clinical suspicion remains, or to document seroconversion.
- Additional testing: If symptoms develop earlier than two weeks, PCR of skin biopsy or joint fluid may be considered, but blood PCR lacks sensitivity and is not recommended for routine diagnosis.
Guidelines from major health agencies advise against testing before the two‑week mark because the absence of detectable antibodies would be misleading. If the bite occurred in a region where Borrelia is endemic and the patient exhibits erythema migrans or systemic signs, treatment may be initiated without waiting for laboratory confirmation. In asymptomatic individuals, the described schedule provides the most reliable detection of a humoral response.