What is the test called after a tick bite? - briefly
The diagnostic evaluation after a tick bite is typically a Lyme disease serology, beginning with an ELISA test and, if positive, confirmed by a Western‑blot assay.
What is the test called after a tick bite? - in detail
After a bite from a hard‑tick, clinicians usually order a two‑step serologic evaluation to detect infection with Borrelia burgdorferi, the agent of Lyme disease. The first tier is an enzyme‑linked immunosorbent assay (ELISA) that screens for IgM and IgG antibodies. A positive or equivocal ELISA result triggers the second tier, a Western blot, which confirms the presence of specific antibody bands. The combination of ELISA followed by Western blot constitutes the standard Lyme disease diagnostic protocol.
Timing of specimen collection influences test performance. Antibodies typically appear 2–4 weeks after the bite; testing earlier may yield false‑negative results. When early localized disease is suspected (e.g., erythema migrans), clinicians may forego serology and treat empirically, reserving laboratory confirmation for later stages or atypical presentations.
In addition to Lyme serology, other tick‑borne pathogens may be screened:
- Anaplasma phagocytophilum – PCR on whole blood or serology (IgG rise in paired samples).
- Babesia microti – Thick‑blood‑smear microscopy, PCR, or indirect immunofluorescence assay.
- Rickettsia rickettsii (Rocky Mountain spotted fever) – Immunofluorescence assay for IgM/IgG; PCR on skin biopsy or blood in acute phase.
- Ehrlichia chaffeensis – PCR or serology with a four‑fold rise in IgG titers.
When a patient presents with systemic symptoms (fever, headache, myalgia) after a tick encounter, a broad panel of tests may be ordered simultaneously. Laboratories often provide multiplex PCR panels that detect DNA from several tick‑borne organisms in a single assay, reducing turnaround time.
Interpretation of results requires attention to pre‑test probability. A positive ELISA with a negative Western blot does not confirm infection; repeat testing or alternative methods (e.g., PCR from skin biopsy of the rash) may be necessary. Conversely, a negative serology in the first weeks post‑exposure should not exclude disease; clinical judgment guides treatment decisions.
Follow‑up testing is recommended for patients with persistent or worsening symptoms. Paired serology collected 2–4 weeks apart can demonstrate seroconversion. Documentation of antibody titers, PCR cycle thresholds, and clinical response provides a comprehensive picture of infection status and informs therapeutic adjustments.