IgM B. afzelii

Positive (clearly above the cut-off)

What it means: A positive IgM response to Borrelia afzelii suggests a recent or early infection with this subspecies of the Lyme bacterium. B. afzelii is more commonly found in Europe and is often associated with skin manifestations of Lyme borreliosis, such as acrodermatitis chronica atrophicans (ACA) and other chronic skin changes.

Important to know: A positive IgM result should always be interpreted with other Lyme tests, clinical history, and symptoms before a diagnosis is made.

IgM B. afzelii measures early antibodies against Borrelia afzelii, a major cause of Lyme disease in Europe and Asia. Unlike B. burgdorferi sensu stricto, which dominates in North America, B. afzelii is strongly linked to skin-related forms of Lyme borreliosis, including erythema migrans and acrodermatitis chronica atrophicans (ACA). IgM antibodies typically appear within the first weeks of infection, making this marker useful for detecting recent or early exposure, especially in patients with skin or joint symptoms after tick bites. Because low-level or isolated IgM responses can reflect cross-reactivity or false positives, results should always be interpreted with other Borrelia markers, clinical history, and follow-up testing.

If your result is Equivocal or Borderline (close to the cut-off):

What it means: Borderline levels of IgM antibodies were detected against Borrelia afzelii. This may represent an early or low-level immune response, or it may reflect non-specific reactivity rather than true Lyme infection. Results in this range require careful interpretation, particularly if you have Lyme-like symptoms or known tick exposure.

Next steps: Your doctor may recommend repeat testing after a few weeks, reviewing other Lyme antibody markers (including B. burgdorferi and B. garinii), or confirming with an immunoblot. Clinical history and symptoms are essential to determine whether this finding represents Lyme disease.

Next Steps for an Equivocal Result

• Repeat testing: Because IgM antibodies may rise in the early weeks after infection, repeating the test in 2–4 weeks can help clarify whether the immune response is increasing (suggesting infection) or fading (suggesting no infection).

• Additional Lyme tests: Your doctor may order IgG antibody testing, immunoblots, or a broader Lyme panel (including other Borrelia subspecies and Osp proteins) to confirm the result.

• Consider co-infections: If exposure risk is high, testing for tick-borne co-infections (e.g., Babesia, Bartonella, Ehrlichia) may also be recommended.

• Clinical evaluation: Symptoms and history of tick exposure are critical. Even borderline results can be significant if you have classic Lyme signs such as erythema migrans, joint pain, neurological changes, or unexplained fatigue.

• Ongoing monitoring: If symptoms persist but results remain unclear, your provider may recommend ongoing monitoring and possibly other diagnostic methods such as PCR.