Lyme Disease Serology: IgG Positive, IgM Negative
A positive IgG with negative IgM indicates either past Lyme disease infection (with persistent antibodies after treatment) or late-stage Lyme disease (>30 days of symptoms), but interpretation depends critically on your clinical symptoms, exposure history, and geographic risk factors. 1
Understanding the Antibody Timeline
The IgG response in Lyme disease generally follows IgM and involves antibodies against a larger number of bacterial antigens. Most patients develop a detectable IgG response beyond 30 days of infection, at which point IgG Western immunoblot alone is typically sufficient for diagnosis. 1
- IgM appears first during early infection (first 4 weeks) and is directed at the most immunogenic antigens 1
- IgG develops later and persists, often for months to years even after successful treatment 2
- After 30 days of symptoms, IgM testing is unnecessary and actually increases the risk for false-positive results 1
Clinical Interpretation Framework
If You Have Current Symptoms (>30 Days Duration):
Your positive IgG could represent active late-stage Lyme disease if you have:
- Lyme arthritis (joint swelling, particularly large joints like the knee) 1
- Late neurologic manifestations (peripheral neuropathy, encephalopathy) 1
- History of tick exposure in an endemic area 1
The diagnosis requires both positive serology AND compatible clinical findings—serology alone does not confirm active infection. 2
If You Are Asymptomatic or Have Non-Specific Symptoms:
Your positive IgG most likely represents past infection with persistent antibodies. This is a critical distinction because:
- Borrelia serology remains positive for months or years in approximately 20% of healthy patients who had Lyme disease in the past 2
- Positive serology as a single diagnostic tool has very limited value and should only support clinically suspected cases 2
- Positive IgG antibodies in healthy individuals with nonspecific symptoms do not warrant antibiotic treatment 2
Geographic and Exposure Context Matters Critically
Even with positive serology, if you live in or only traveled to non-endemic areas, the positive result likely represents a false positive rather than true Lyme disease. 1
- In low-incidence states, the positive predictive value of Lyme serology is only 10% for patients without recent travel to endemic regions 1
- Only 0.7% of patients without endemic area exposure who had signs of disseminated infection (arthritis, cranial neuropathies, meningitis) actually had Lyme disease 1
Common Pitfalls to Avoid
Do not misinterpret your results based on band patterns alone. 1
- A positive IgG requires ≥5 of 10 specific bands (18,21-24,28,30,39,41,45,58,66, and 93 kDa) 1
- Fewer than 5 IgG bands does NOT indicate a positive result 1
- The 41-kDa band alone is particularly prone to cross-reactivity with other bacterial flagellar proteins and was found in 43% of healthy controls 1
Avoid unnecessary antibiotic treatment based on serology alone. 2, 3
- False-positive IgM results have led to unnecessary antibiotic treatment in 78% of affected patients in clinical practice 3
- Long-term or cycling antibiotic regimens for positive serology without objective clinical disease are not beneficial 2
Next Steps
If you have compatible symptoms >30 days duration AND endemic area exposure:
- Your positive IgG supports the diagnosis of late Lyme disease
- Treatment is indicated based on the specific manifestation (arthritis, neuroborreliosis, etc.) 1
If you are asymptomatic or have only nonspecific symptoms:
- No treatment is indicated 2
- The positive IgG likely represents past infection with antibody persistence
- Consider alternative diagnoses for your current symptoms 1
If you have symptoms <30 days with erythema migrans rash: