When should blood be drawn for infections after a tick bite? - briefly
Obtain a serum sample at the appearance of a rash or systemic symptoms, usually 2–3 weeks after the bite, to assess for early Lyme disease. Collect a convalescent specimen 4–6 weeks later to confirm seroconversion, and follow the same schedule for other tick‑borne infections such as anaplasmosis or ehrlichiosis.
When should blood be drawn for infections after a tick bite? - in detail
Blood sampling for tick‑borne infections must be timed to match pathogen biology and the patient’s clinical picture.
If fever, rash, headache, myalgia, or arthralgia appear within days of the bite, draw blood immediately for:
- PCR or culture for Anaplasma phagocytophilum and Ehrlichia chaffeensis (detectable within the first week).
- PCR for Babesia microti (positive in the acute phase).
- Serology for Rocky‑Mountain spotted fever (IgM may rise after 5–7 days).
When the bite is asymptomatic or symptoms develop later, schedule draws according to the expected seroconversion window:
- Lyme disease: obtain a sample 2–3 weeks after exposure for IgM ELISA; repeat at 4–6 weeks if the first test is negative but clinical suspicion persists. Consider a second draw 6–12 weeks for IgG confirmation.
- Tick‑borne encephalitis: collect serum and cerebrospinal fluid 7–14 days after neurologic signs for IgM; a convalescent sample at 4–6 weeks for IgG assessment.
- Bartonella henselae (rarely transmitted by ticks): draw at 1–2 weeks for PCR; repeat at 4 weeks for serology if initial result is negative and symptoms continue.
For patients receiving prophylactic doxycycline after a confirmed tick attachment >36 hours, a baseline blood draw is not required unless symptoms emerge. If treatment is delayed or absent, obtain baseline specimens before initiating antibiotics to allow post‑treatment comparison.
In cases of persistent or relapsing illness, repeat sampling at 2‑week intervals until the pathogen is identified or ruled out. Document the date of the bite, symptom onset, and any antimicrobial therapy, as these factors influence test sensitivity.