When should a blood test for borreliosis be taken after a tick bite?

When should a blood test for borreliosis be taken after a tick bite? - briefly

A serologic test is typically scheduled 2–4 weeks after the bite, when specific antibodies are usually detectable; earlier testing (1–2 weeks) may be warranted only if clinical symptoms arise.

When should a blood test for borreliosis be taken after a tick bite? - in detail

Serologic testing for Lyme disease should be timed to coincide with the expected appearance of antibodies. After a bite, the immune response typically becomes detectable between the third and sixth week. Consequently, the first blood sample is usually drawn no earlier than four weeks post‑exposure. Testing before this window often yields false‑negative results because IgM and IgG antibodies have not yet reached measurable levels.

If the initial test is negative and the patient develops characteristic signs—such as a rash, fever, arthralgia, or neurologic symptoms—repeat sampling is advised at eight to twelve weeks. A second draw allows detection of a rising antibody titer, confirming infection that may have been missed initially.

When early localized disease manifests as a classic expanding erythema, clinicians often forgo serology and initiate treatment based on clinical presentation. In cases of disseminated or late disease, a two‑step testing algorithm (ELISA followed by confirmatory Western blot) is standard. Molecular methods, such as PCR, are reserved for cerebrospinal fluid or synovial specimens and are not routinely used for blood screening.

Key timing considerations:

  • First draw: ≥ 4 weeks after the bite, preferably at 4–6 weeks.
  • Second draw (if needed): 8–12 weeks post‑bite, especially when symptoms emerge after the initial test.
  • Immediate treatment: Initiated without testing when the rash is present or high clinical suspicion exists.

The recommended schedule balances the biological lag in antibody production with the need for prompt diagnosis, minimizing false‑negative outcomes while ensuring timely therapeutic intervention.