What is the blood test called after a tick bite? - briefly
The standard laboratory evaluation after a tick bite is a Lyme disease serologic panel, beginning with an ELISA test and confirmed by a Western blot if positive. It detects antibodies against Borrelia burgdorferi.
What is the blood test called after a tick bite? - in detail
The laboratory assay ordered after a tick exposure is the Lyme disease serologic panel. The panel typically begins with an enzyme‑linked immunosorbent assay (ELISA) that detects immunoglobulin M and G antibodies against Borrelia burgdorferi. If the ELISA result is positive or equivocal, a confirmatory Western blot is performed to identify specific protein bands.
Key points for clinicians:
- Timing: Antibodies usually become detectable 2–4 weeks after the bite. Testing earlier may yield false‑negative results; repeat testing after 4 weeks is recommended if initial study is negative but clinical suspicion remains.
- Sample: Venous whole blood collected in a serum separator tube; serum is used for both ELISA and Western blot.
- Interpretation:
- Positive ELISA with a positive Western blot (≥5 of 10 IgG bands or ≥2 of 3 IgM bands) confirms infection.
- Positive ELISA with a negative Western blot is considered indeterminate; repeat testing is advised.
- Negative ELISA essentially rules out recent infection, provided the test is performed after the seroconversion window.
Other tick‑borne pathogens may require separate assays:
- Anaplasma phagocytophilum: Polymerase chain reaction (PCR) on whole blood or serology (IgG rise between acute and convalescent samples).
- Babesia microti: Thick‑blood‑smear microscopy, PCR, or indirect immunofluorescence assay for IgG antibodies.
- Ehrlichia chaffeensis: PCR or indirect immunofluorescence assay; serology similar to Anaplasma.
When multiple agents are possible, a multiplex PCR panel can simultaneously detect DNA from Borrelia, Anaplasma, Ehrlichia, and Babesia.
Laboratories often provide a reflex protocol: an initial ELISA triggers automatic Western blot if the result exceeds the cutoff, reducing turnaround time.
In summary, the standard diagnostic work‑up after a tick bite begins with an ELISA for Lyme disease, followed by a confirmatory Western blot, with additional PCR or serologic tests employed for other common tick‑borne infections.