Lyme antibody (Borrelia serology)

This test detects antibodies the immune system makes against Borrelia burgdorferi (and related species), the bacteria that cause Lyme disease, transmitted by the bite of an infected tick. It does not detect the bacterium directly but the body's antibody response to it. To reduce false positives, it is done as a two-tier scheme: a sensitive screening test (an ELISA) is performed first, and only if that is positive or borderline is a more specific confirmatory test (a Western blot, or a second-generation antibody test) run. The interpretation depends heavily on timing and context. In the first days to weeks of infection — the stage of the classic expanding 'bull's-eye' rash — antibodies may not yet have developed, so a negative test does not rule out early Lyme, and the rash alone is enough to treat. Later features, such as joint, nerve or heart involvement, are usually accompanied by clear antibodies. A key caveat is that, once formed, antibodies can persist for months or years after successful treatment, so a positive test cannot by itself distinguish current from past infection, and the test should not be used to monitor treatment or to test people without a compatible illness. Lyme serology is therefore a support to a clinical diagnosis, not a stand-alone answer.

• A positive two-tier result — supports exposure to the Lyme bacterium, read alongside symptoms and tick exposure.
• Later-stage Lyme disease — joint, nerve or heart involvement usually shows clear antibodies.
• Past, treated infection — antibodies can persist for years, so a positive test does not always mean current disease.
• A false-positive screening test — why the confirmatory second tier is essential.

• Negative — the expected result; no antibodies detected.
• Very early infection — antibodies may not have formed yet, so early Lyme with the classic rash is treated on the clinical picture regardless.
• No exposure — no evidence of Lyme.