When after a tick bite should blood be tested for Lyme disease and encephalitis? - briefly
«Blood serology for Borrelia is indicated 2–4 weeks after the bite when rash or systemic symptoms are absent, with repeat testing if signs persist». «Testing for encephalitis is reserved for the appearance of neurological symptoms, typically emerging several weeks to months post‑exposure».
When after a tick bite should blood be tested for Lyme disease and encephalitis? - in detail
Blood testing for Borrelia burgdorferi after a tick exposure should be timed to match the development of the immune response. Serologic assays that detect IgM antibodies become reliable approximately 2 weeks after the bite, reach peak sensitivity around 3–4 weeks, and decline thereafter. IgG antibodies appear later, usually 4–6 weeks post‑exposure, and remain detectable for months. Consequently, a two‑stage approach is advisable:
- Day 0–13: refrain from serology; clinical assessment dominates because antibodies are rarely present.
- Day 14–27: obtain IgM‑focused ELISA or immunoblot; positive results support early infection, but negative findings do not exclude disease.
- Day 28 and beyond: perform combined IgM/IgG testing; a positive IgG result confirms established infection, while persistent IgM without IgG may indicate a false‑positive or early stage.
Testing for neuroborreliosis (Lyme‑associated encephalitis) follows a similar kinetic pattern but requires additional considerations. Cerebrospinal fluid (CSF) analysis, including Borrelia PCR and intrathecal antibody synthesis, is the definitive diagnostic tool. Serum testing can aid interpretation when performed after the same interval as IgG serology (≥ 4 weeks). Early CSF PCR sensitivity is limited; therefore, blood tests taken before the fourth week are unlikely to contribute to the diagnosis of encephalitis.
Guideline summaries:
- Do not order serology within the first two weeks unless a clear clinical indication exists.
- Schedule the first serum test at the end of the second week to capture IgM.
- Repeat or extend testing after the fourth week to detect IgG and to correlate with CSF findings for neurological involvement.
- Recognize that false‑negative results are common before antibody maturation; repeat testing may be necessary if symptoms persist.
Adhering to these intervals maximizes diagnostic yield while minimizing unnecessary investigations.