Lyme Disease Diagnosis Guidelines

Diagnostic Criteria

The Centers for Disease Control and Prevention (CDC) recommends a two-tiered testing approach that requires specific band thresholds to be met for diagnosing Lyme disease, including ≥2 of 3 specific bands for IgM Western blot positivity and ≥5 of 10 specific bands for IgG Western blot positivity 1, 2, 3
The CDC-recommended IgM Western blot positivity criteria do not include the 58 kDa band, and a single band of any type does not constitute a positive result 1, 2, 3
The CDC-recommended IgG Western blot positivity criteria include the 58 kDa band, but require at least 4 additional bands for positivity 1, 2

For patients with symptoms lasting less than 30 days, the CDC recommends performing a first-tier EIA/ELISA, followed by reflex to both IgM and IgG Western blot if positive or equivocal, and applying strict band criteria for positivity 1, 3
For patients with symptoms lasting more than 30 days, the CDC recommends performing a first-tier EIA/ELISA, followed by reflex to IgG Western blot only if positive or equivocal, as IgM testing beyond 4-8 weeks of symptoms is not clinically interpretable 1, 3, 4, 5

The presence of a single IgM band or less than 5 IgG bands does not indicate a positive result, and misinterpreting Western blots with insufficient bands as positive is a common diagnostic error 2, 3, 6
IgM testing beyond 4-8 weeks of symptoms is not clinically interpretable and should not be performed, as antibodies persist for months to years after treatment 4, 5

Patients with erythema migrans rash and appropriate epidemiologic exposure can be diagnosed clinically without serologic confirmation, as early Lyme disease serology has decreased sensitivity in the first weeks of infection 4, 7, 8, 5
Treatment should not be delayed awaiting serologic confirmation in patients with characteristic erythema migrans, and alternative diagnoses should be pursued based on the clinical presentation if serology is negative 4, 5, 1, 2, 3

A solitary 41 kDa IgG band (targeting Borrelia burgdorferi flagellin) is not diagnostic for Lyme disease because it cross‑reacts with flagellar proteins of many non‑Borrelial bacteria and was detected in ≈ 43 % of healthy individuals without Lyme exposure. 9

The CDC defines a positive IgG Western blot only when ≥ 5 of the 10 CDC‑specified bands are present; the presence of fewer than five bands, including an isolated 41 kDa band, does not meet criteria for a positive result. 9
The CDC‑recommended algorithm requires a positive or equivocal first‑tier EIA/ELISA before proceeding to Western blot; performing a Western blot without a preceding positive screening test is considered a diagnostic error. 10

In patients with strong clinical suspicion of early Lyme disease (symptom duration < 30 days), the guideline advises repeat serologic testing in 2–4 weeks to allow antibody development, rather than relying on a single reactive 41 kDa band. [10][11]12

Interpreting a single 41 kDa IgG band as evidence of infection reduces test specificity and increases the risk of misdiagnosis; such a result should be reported as negative according to CDC criteria. 9