How long after a tick bite should a Borrelia test be taken? - briefly
Serologic testing is recommended at least 2–3 weeks after the bite, when antibodies are typically detectable. If the first result is negative and symptoms appear, a repeat test at 4–6 weeks is advisable.
How long after a tick bite should a Borrelia test be taken? - in detail
A Borrelia infection typically becomes detectable in blood after a latency period that follows the bite. The earliest serological markers appear about 2 weeks post‑exposure; IgM antibodies may be present from day 7 to day 30, while IgG antibodies usually emerge after day 30 and persist. Consequently, the first reliable antibody test should be performed no sooner than 14 days after the bite. Testing before this window yields a high false‑negative rate because the immune response has not yet matured.
When early disease is suspected—e.g., erythema migrans or flu‑like symptoms—polymerase chain reaction (PCR) on skin biopsy or joint fluid can detect bacterial DNA within days of the bite. PCR is not routinely used for blood specimens because sensitivity is low in early infection.
If the initial serology performed at 2–4 weeks is negative but clinical suspicion remains, a repeat test after 4–6 weeks is advisable. A second sample allows detection of IgG seroconversion, which confirms infection that was missed in the first assay.
Key timing considerations:
- Day 0–7: No reliable blood test; consider PCR from skin lesion if present.
- Day 7–14: IgM may be emerging; results still unreliable for definitive diagnosis.
- Day 14–30: First appropriate serology; IgM detection possible, IgG may appear.
- Day 30+: IgG detection reliable; repeat testing if earlier result was negative and symptoms persist.
Clinical guidelines recommend initiating empiric treatment for early localized disease when characteristic rash is present, without waiting for laboratory confirmation. In the absence of rash, testing should follow the schedule above, and treatment decisions should be based on both laboratory results and symptomatology.