When a person becomes infected with Borrelia burgdorferi, the bacterium that causes Lyme disease, the body’s immune system mounts a defense by producing special proteins called antibodies. The two main types involved are IgM and IgG antibodies. Each type plays a unique role depending on when the infection occurs.
IgM antibodies are the immune system’s first responders. They usually appear within 3 to 6 weeks after infection begins. In early Lyme disease, these antibodies can be detected in the blood and suggest a recent or ongoing infection. However, IgM antibodies can sometimes be misleading. They may cross-react with other illnesses, meaning someone could test positive for Lyme disease even if they have a different infection. This risk of “false positives” makes it crucial to interpret IgM results carefully, especially if symptoms do not clearly match Lyme disease.
IgG antibodies take longer to develop, often peaking months after infection starts. Their presence signals that the body has been exposed to the bacteria for a while. In late-stage Lyme disease, where symptoms might include arthritis, heart issues, or nerve problems, IgG is usually the dominant antibody found. Unlike IgM, IgG antibodies tend to offer stronger proof of past or persistent infection. However, they can stay in the blood for many years, even after successful treatment. Therefore, a positive IgG test does not necessarily mean a person currently has active Lyme disease.
For patients, understanding this dynamic is crucial. Testing positive for Lyme disease antibodies does not always mean immediate treatment is needed. Many people retain antibodies long after their infection has cleared, and unnecessary antibiotic use can cause harm. Doctors often focus more on current symptoms and history rather than relying solely on blood tests.
This panel is particularly useful if you’ve been in areas where Lyme-carrying ticks are common and are experiencing symptoms such as fever, rash (especially a bull’s-eye rash), muscle aches, or neurological changes. While a positive test suggests an immune response to the infection, results often need confirmation with more specific testing like a Western blot. Early detection is key—treatment with antibiotics is most effective when started promptly, and this screen provides the first step in identifying whether Lyme disease could be the cause of your symptoms.
