When should a Borrelia test be taken after a tick bite in a child? - briefly
A Lyme serology is indicated only if the child shows erythema migrans or systemic symptoms, generally 2–4 weeks after the bite. Testing before this interval often produces false‑negative results because antibodies have not yet developed.
When should a Borrelia test be taken after a tick bite in a child? - in detail
Testing for Lyme disease in a child who has been bitten by a tick should be timed according to the expected development of detectable antibodies. The immune response typically becomes measurable 2–4 weeks after the bite. Performing an enzyme‑linked immunosorbent assay (ELISA) before this window yields a high likelihood of false‑negative results because seroconversion has not yet occurred.
If the child exhibits early localized signs—such as an erythema migrans rash—clinical diagnosis is sufficient and laboratory confirmation is not required. In the absence of objective findings, a blood sample collected at least 21 days post‑exposure is recommended. A second sample taken 4–6 weeks after the bite can confirm seroconversion if the initial test was negative but symptoms develop later.
When testing is indicated, the standard two‑step algorithm applies:
- First‑line ELISA to detect IgM and IgG antibodies.
- Confirmatory Western blot performed only if ELISA is positive or equivocal.
For children under 5 years, IgM responses may be less robust; therefore, clinicians often rely on repeat testing or clinical judgment. In cases of disseminated disease—neurologic, cardiac, or arthritic manifestations—serologic testing can be performed at any time because antibodies are usually present.
Guidelines from major infectious disease societies advise against routine testing within the first two weeks after a bite unless the child presents with overt rash or systemic symptoms. Testing earlier than 3 weeks should be reserved for high‑risk situations, such as prolonged attachment (>24 hours) in endemic areas, and should be accompanied by a repeat sample after the seroconversion window.
In summary, the optimal period for obtaining a Lyme serology in a pediatric tick‑bite exposure is 3–4 weeks after the incident, with a follow‑up draw at 6 weeks if initial results are negative and clinical suspicion persists. Immediate testing is only justified when clear clinical evidence of infection exists.