When can I have blood tested for borreliosis after a tick bite? - briefly
A blood test for Lyme disease is usually reliable 2–4 weeks after the bite, when antibodies have had time to develop; if early symptoms such as rash or flu‑like signs appear, testing can be performed sooner, but a negative result may be inconclusive.
When can I have blood tested for borreliosis after a tick bite? - in detail
After a tick attachment, antibodies against the bacterium that causes Lyme disease typically become detectable two to four weeks later. Testing before this period usually yields a negative result because the immune response has not yet produced measurable levels of IgM or IgG.
If a characteristic erythema migrans rash appears, treatment can begin without laboratory confirmation; a blood sample taken at the time of diagnosis is still useful for baseline documentation. In the absence of a rash, serologic testing is recommended only when systemic signs such as fever, headache, fatigue, arthralgia, or neurological symptoms develop, and it should be performed at least 14 days after the bite.
The usual schedule for laboratory evaluation is:
- Day 0–13: No serology; antibodies are unlikely to be present. Consider prophylactic doxycycline if the tick was attached for ≥ 36 hours and local infection rates are high.
- Day 14–30: First‑line ELISA (or equivalent immunoassay). A positive result is followed by a confirmatory Western blot.
- Day 31 and beyond: Repeat serology if the initial test was negative but clinical suspicion persists or new symptoms arise. Late‑stage disease may show IgG dominance, which can be detected reliably after one month.
Polymerase chain reaction (PCR) testing of blood is rarely useful because spirochetemia is transient; PCR is reserved for cerebrospinal fluid or synovial fluid when neuroborreliosis or Lyme arthritis is suspected.
In summary, arrange a blood draw for Lyme disease antibodies no earlier than two weeks post‑exposure, and repeat after one month if early testing was negative but the patient remains symptomatic. Immediate testing is only justified when a clear rash is present, in which case treatment should not be delayed.