Lyme Ab (IgM) is a blood test that detects immunoglobulin M antibodies directed against Borrelia burgdorferi, the bacterium that causes Lyme disease. Lyme disease is a tick-borne illness transmitted primarily by black-legged ticks (Ixodes species), which are commonly found in wooded or grassy areas across North America and parts of Europe.
IgM antibodies are typically the first antibodies produced by the immune system when the body encounters a new infection. In Lyme disease, IgM antibodies usually become detectable within 1–3 weeks after infection, making this test particularly useful for identifying early-stage Lyme disease.
During the early phase of infection, individuals may experience symptoms such as:
-
Fever and chills
-
Fatigue
-
Headache
-
Muscle or joint aches
-
Swollen lymph nodes
-
The characteristic erythema migrans rash (often described as a bull’s-eye rash)
If Lyme disease progresses without treatment, the infection can spread to other parts of the body, leading to complications such as:
-
Facial nerve palsy (Bell’s palsy)
-
Nerve pain or numbness
-
Heart rhythm disturbances (Lyme carditis)
-
Joint inflammation and arthritis
Because IgM antibodies are associated with recent infection, they typically rise during the first several weeks of illness and may decline later as IgG antibodies develop. For this reason, IgM results are most informative when symptoms have been present for less than 30 days.
Testing for Lyme disease is commonly performed using a two-step approach. An initial screening immunoassay (IA or EIA) detects antibodies, and positive or equivocal results may be followed by a confirmatory immunoblot (Western blot) or other supplemental testing. Interpreting Lyme antibody results requires consideration of symptoms, timing of exposure, geographic risk, and clinical findings.
Early detection and treatment—usually with antibiotics—can significantly reduce the risk of long-term complications from Lyme disease.
LYME AB (IGM)
Every lab result you’ve ever had, charted and explained.
Healthmatters is a tracker for your lab results. Upload a report from any lab, any country — every marker charted and explained.
Start with my report →
All our content is backed by peer-reviewed studies, academic research, and trusted medical sources. We’re committed to accuracy and transparency — see our editorial policy for details.