The IgG Immunodominant Peptide C6 (P. C6) test detects antibodies against a highly conserved region of the VlsE protein from Borrelia burgdorferi, the main bacterium that causes Lyme disease. The C6 peptide is considered an immunodominant epitope—a portion of the protein that triggers a strong and reliable immune response across different strains of Borrelia.
What IgG P. C6 Means
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IgG antibodies to C6 usually appear several weeks after infection and remain detectable during later stages of Lyme disease.
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A positive result suggests past or ongoing immune recognition of Borrelia, making this test useful for identifying later-stage or persistent infection.
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Because C6 is highly conserved, the test can detect antibody responses across different Borrelia species, improving diagnostic sensitivity.
Clinical Importance
Testing for IgG P. C6 can be particularly valuable in:
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Patients with suspected Lyme disease who are beyond the early infection window
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Individuals with joint, neurological, or chronic symptoms linked to Lyme
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Confirmatory testing, as C6 is often used alongside other Borrelia markers (OspC, OspA, VlsE) to increase accuracy
Patient Takeaway
A positive IgG P. C6 result means your immune system has recognized the C6 peptide of Borrelia, suggesting exposure to the Lyme disease bacterium. This does not always prove an active infection, since IgG can persist after prior illness, but it is considered a reliable marker of Borrelia exposure.
Your healthcare provider will compare this result with your symptoms, tick exposure history, and other Lyme disease tests for a complete interpretation.
If your result is equivocal (borderline), antibody levels are close to the cutoff and the finding is uncertain. In this case, repeat or additional confirmatory testing may be recommended.
IgG Immunodominant P. C6
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