When are tests conducted after a tick bite suspected of causing Lyme disease? - briefly
Testing is typically performed 2–4 weeks after a suspected tick exposure, when serologic antibodies become detectable; in cases with early localized symptoms, clinicians may also order PCR or culture of the bite site. If initial serology is negative but symptoms persist, repeat testing after another 2–3 weeks is recommended.
When are tests conducted after a tick bite suspected of causing Lyme disease? - in detail
Diagnostic evaluation after a tick bite that raises suspicion for Lyme disease depends on the interval between exposure and symptom onset. In the first two weeks, the immune response is typically insufficient to generate detectable antibodies; therefore, direct detection methods are preferred. Polymerase chain reaction (PCR) on skin biopsy of an erythema migrans lesion, or on joint fluid when arthritis is present, provides the most reliable early confirmation. Blood culture for Borrelia burgdorferi is rarely used because of low sensitivity.
From the third to the sixth week post‑exposure, serologic testing becomes informative. Enzyme‑linked immunosorbent assay (ELISA) is performed first; a positive result is confirmed with a Western blot. IgM antibodies usually appear between weeks 3 and 6, while IgG antibodies develop after week 6 and persist longer. A single negative serology within this window does not exclude infection if clinical signs are evident; repeat testing after an additional two‑week interval is recommended.
If the initial evaluation is negative and the patient remains asymptomatic, no further testing is required. Should symptoms such as fever, arthralgia, or neurologic signs emerge later, a repeat serologic panel should be obtained, and PCR of cerebrospinal fluid may be indicated for neurologic involvement.
Special populations—children, pregnant individuals, and immunocompromised patients—may exhibit delayed or diminished antibody production. In these groups, clinicians often rely on a combination of early PCR and later serology, with a lower threshold for repeat testing.
Testing timeline summary
- 0–2 weeks: PCR of lesion or joint fluid; serology generally not reliable.
- 3–6 weeks: ELISA followed by Western blot; IgM detection possible.
- >6 weeks: ELISA/Western blot focusing on IgG; consider repeat serology if initial result was negative but symptoms persist.
- Any time with new symptoms: Repeat serology and consider PCR of appropriate specimens (CSF for neurologic signs).
Adherence to this schedule aligns diagnostic sensitivity with the pathogen’s biological progression, ensuring timely identification and treatment of Lyme disease.