What tests should be performed when a tick bites? - briefly
Order serologic testing for Borrelia antibodies, PCR assays for tick‑borne pathogens, and a complete blood count with differential to detect inflammatory response. Include multiplex PCR panels to screen for Anaplasma, Ehrlichia, and Babesia co‑infections.
What tests should be performed when a tick bites? - in detail
After a tick attachment, a systematic evaluation should begin with a thorough clinical history and physical examination. Information on the tick’s species, the length of attachment, and the geographic region where the bite occurred guides the selection of laboratory investigations.
The initial laboratory panel includes:
- Complete blood count – detects leukocytosis, thrombocytopenia, or anemia that may signal an early systemic response.
- Liver function tests – assess elevations in alanine aminotransferase or aspartate aminotransferase, common in several tick‑borne infections.
- Serum creatinine and electrolytes – monitor renal involvement, particularly in severe rickettsial disease.
Serologic testing focuses on the most prevalent pathogens:
- Enzyme‑linked immunosorbent assay for antibodies against Borrelia burgdorferi – performed as an initial screen.
- Confirmatory immunoblot – required when the screening assay yields a positive result.
- Indirect immunofluorescence assay for Anaplasma phagocytophilum and Ehrlichia chaffeensis – indicated if fever, leukopenia, or thrombocytopenia are present.
- Immunoglobulin M and G ELISA for Rickettsia rickettsii – useful in regions where spotted‑fever rickettsiosis is endemic.
- Serology for Babesia microti – performed when hemolytic anemia or hemoglobinuria occurs.
Molecular diagnostics complement serology, especially during the early phase of infection when antibodies may be absent:
- Polymerase chain reaction on whole blood for Borrelia DNA – increases sensitivity within the first weeks after exposure.
- PCR for Anaplasma and Ehrlichia – recommended for patients with compatible clinical signs and a high pre‑test probability.
- PCR for Babesia – indicated when microscopic examination of blood smears reveals intra‑erythrocytic parasites.
Additional tests may be required based on specific exposure risks:
- Reverse‑transcriptase PCR for Powassan virus – considered for neurological symptoms following a bite in endemic areas.
- Culture or serology for Francisella tularensis – reserved for bites occurring in known tularemia hotspots.
- Antigen detection for Coxiella burnetii – seldom needed but possible in occupational exposures.
Timing of specimen collection influences interpretation. Acute samples are drawn within 1–2 weeks of the bite; convalescent samples are collected 2–4 weeks later to detect seroconversion. Persistent or worsening symptoms merit repeat testing and consultation with infectious‑disease specialists.
Prompt initiation of appropriate antimicrobial therapy, guided by test results and epidemiologic context, reduces the risk of complications. Empiric doxycycline remains the first‑line agent for most suspected tick‑borne infections pending definitive laboratory confirmation.