What should be tested in blood after a tick bite? - briefly
After a tick exposure, order serologic testing for Borrelia burgdorferi (ELISA with confirmatory Western blot) and assays for Babesia microti, Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Rickettsia rickettsii, plus PCR for Powassan virus where indicated. Include a complete blood count with differential to detect thrombocytopenia or leukopenia that may signal other tick‑borne infections.
What should be tested in blood after a tick bite? - in detail
After a tick attachment, laboratory evaluation should focus on the pathogens most frequently transmitted by the species present in the region and on the physiological effects of the bite. The work‑up typically includes:
- Serologic screening for Lyme disease – initial enzyme‑linked immunosorbent assay (ELISA) followed by confirmatory immunoblot if positive. Repeat testing after 2–4 weeks may be required for seroconversion.
- Molecular detection of Anaplasma phagocytophilum – polymerase chain reaction (PCR) on whole blood, especially during the first week of illness.
- Babesia microti assessment – thick and thin blood smears examined for intra‑erythrocytic parasites; PCR provides higher sensitivity when parasitemia is low.
- Ehrlichia chaffeensis testing – PCR for early infection; indirect immunofluorescence assay (IFA) or ELISA for later stages.
- Rickettsia rickettsii and other spotted‑fever group agents – IFA serology, paired acute and convalescent samples spaced 2–3 weeks apart; PCR may be useful on skin biopsies if rash is present.
- Tick‑borne encephalitis virus – IgM and IgG ELISA; neutralization test for confirmation in endemic areas.
- Additional agents when epidemiologically indicated – PCR or serology for Borrelia miyamotoi, Bartonella henselae, Francisella tularensis, or relapsing fever Borrelia species.
Baseline hematologic and biochemical panels help identify systemic involvement:
- Complete blood count – leukopenia, thrombocytopenia, or anemia suggest ehrlichiosis, anaplasmosis, or babesiosis.
- Liver function tests – elevated transaminases are common in many tick‑borne infections.
- Renal function and electrolytes – monitor for acute kidney injury, especially in severe babesiosis or Rocky Mountain spotted fever.
- Inflammatory markers – C‑reactive protein or erythrocyte sedimentation rate may support a systemic response but are nonspecific.
Timing of specimen collection influences test performance. Acute‑phase samples (≤7 days post‑exposure) are preferred for PCR and blood smears, whereas serologic assays often require a convalescent sample taken 2–4 weeks later to detect rising antibody titers. When clinical suspicion is high and initial tests are negative, repeat or alternative assays should be considered.