How to test for Lyme disease after a tick bite? - briefly
After a tick bite, clinicians typically order a two‑step serology: an ELISA screening test for antibodies against Borrelia burgdorferi. If the ELISA result is positive or equivocal, a Western blot is performed to confirm infection, particularly when the tick was attached for more than 36 hours or early symptoms are present.
How to test for Lyme disease after a tick bite? - in detail
When a tick bite occurs, the first step is to confirm that the arthropod was attached long enough to transmit the bacterium—generally more than 24 hours. Secure removal of the tick reduces further exposure but does not eliminate the risk already incurred.
Testing is indicated if the bite originated from a region where the disease is endemic, if the tick was identified as a known carrier species, or if early symptoms appear (e.g., erythema migrans, fever, chills, fatigue, headache, muscle aches). The timing of specimen collection is critical because antibodies may not be detectable during the initial days after exposure.
Two‑tier serologic algorithm
- Screening assay (ELISA or immuno‑fluorescence) – detects IgM and IgG antibodies against Borrelia burgdorferi antigens. A positive or equivocal result proceeds to confirmatory testing.
- Confirmatory assay (Western blot) – separates bacterial proteins by electrophoresis and identifies specific antibody bands. Interpretation follows CDC criteria: ≥2 of 3 IgM bands (22‑24‑39 kDa) for samples collected ≤30 days, and ≥5 of 10 IgG bands for samples collected >30 days.
Alternative or adjunctive methods
- Polymerase chain reaction (PCR) on synovial fluid, cerebrospinal fluid, or skin biopsy can detect bacterial DNA, useful in late‑stage manifestations where serology may be ambiguous.
- Culture of B. burgdorferi from skin or blood is rarely performed because of low sensitivity and prolonged incubation.
- Multiplex PCR panels are emerging for simultaneous detection of tick‑borne pathogens, but validation varies by laboratory.
Sample collection guidelines
- Draw blood 2–4 weeks after the bite for early‑stage disease; extend to 4–6 weeks for later presentations.
- Use serum or plasma; avoid hemolyzed specimens.
- For PCR, collect tissue from the rash margin or joint aspirate under sterile conditions.
Result interpretation
- A positive two‑tier test confirms exposure; clinical correlation is essential because antibodies may persist after successful treatment.
- Negative serology within the first two weeks does not exclude infection; repeat testing after the appropriate interval if symptoms persist.
- Positive PCR without serologic confirmation suggests active infection, especially in neuroborreliosis or Lyme arthritis.
Follow‑up
- Patients with a confirmed diagnosis receive antibiotic therapy (doxycycline, amoxicillin, or cefuroxime) for 10–21 days, depending on disease stage.
- Re‑testing after treatment is not routinely recommended unless new symptoms emerge.
- Pediatric cases follow the same algorithm, with dosage adjustments for age and weight.
By adhering to the timing, specimen type, and two‑tier testing protocol, clinicians can reliably identify infection after a tick encounter and initiate appropriate management.