How many days after a tick bite should tests be performed? - briefly
Testing for tick‑borne infections should be performed roughly 14–21 days after the bite, with serologic screening for Lyme disease usually drawn at the 2‑week mark and repeated at 4 weeks if initial results are negative. Earlier testing is warranted only if acute symptoms develop.
How many days after a tick bite should tests be performed? - in detail
Testing after a tick attachment should be timed to match the incubation periods of the most common tick‑borne pathogens.
For Lyme disease, the causative bacterium Borrelia burgdorferi typically requires at least 36 hours of attachment before transmission. Serologic testing is unreliable during the first week because antibodies often have not yet formed. The recommended approach is:
- Perform an initial enzyme‑linked immunosorbent assay (ELISA) at 2–3 weeks post‑exposure if an erythema migrans rash is absent.
- If the ELISA is positive, follow with a Western blot for confirmation.
- Repeat serology at 4–6 weeks if the first test is negative but clinical suspicion remains.
For anaplasmosis and ehrlichiosis, the pathogen can appear in the bloodstream within 5–7 days. Polymerase chain reaction (PCR) or peripheral blood smear examination is most effective when obtained between days 5 and 10 after the bite. A second sample at day 14 can capture late‑rising antibodies.
Babesiosis often shows detectable parasites on a smear after 7–14 days. PCR testing is sensitive from day 7 onward; a repeat test at day 21 increases diagnostic yield.
Tick‑borne viral infections such as Powassan virus have a longer incubation (1–5 weeks). Serology or PCR should be ordered no earlier than day 14, with a convalescent sample taken 2–4 weeks later to document seroconversion.
In summary:
- Day 0–3: No reliable serology; monitor for rash or systemic signs.
- Day 5–10: PCR or blood smear for anaplasmosis, ehrlichiosis, early babesiosis.
- Day 14–21: ELISA for Lyme disease; PCR/serology for Babesia and viral agents.
- Day 28+: Repeat Lyme serology if initial test negative and symptoms persist; consider convalescent titers for viral infections.
Testing should be aligned with symptom onset and the specific pathogen’s known timeline rather than a single fixed interval.