Can the Western blot diagnose Lyme disease in the first week after a tick bite?

No. Antibody responses take two to four weeks to develop, so Western blot is insensitive in the first weeks of infection. Early Lyme disease with erythema migrans is a clinical diagnosis; if serology is initially negative and suspicion is high, repeat testing in four to six weeks may capture delayed seroconversion.

What does a positive IgM Western blot mean if symptoms have been present for months?

A positive IgM Western blot in a patient with prolonged symptoms is usually a false positive and should not guide treatment. IgM results are clinically valid only in early disease (symptom onset within 30 days); late isolated IgM positivity is common and non-specific.

Why are there different band criteria for IgG and IgM?

IgM responses target a narrow set of early immunodominant antigens (23, 39, 41 kDa), requiring two of three bands for positivity. IgG responses broaden over time to include many surface and flagellar proteins, so five of ten bands are required, reflecting the diversity of late adaptive immunity.

Should the Western blot be repeated to monitor treatment response?

No. Antibody titres do not reliably fall after treatment, and a persistently positive Western blot does not indicate treatment failure or ongoing infection. Repeat serology is not recommended for monitoring cure; clinical improvement is the measure of treatment success.

What does it mean if the Western blot shows bands other than the CDC criteria bands?

Some specialty laboratories report expanded or non-CDC band sets to increase sensitivity, but these criteria are not validated or universally accepted. Practitioners must know which criteria were applied and recognise that expanded band reporting may reduce specificity and is considered exploratory by CDC and IDSA guidelines.

Is fasting required for the Lyme Western blot?

No. The test does not require fasting. Timing relative to symptom onset and any antibiotic therapy is more important for interpretation than pre-test preparation.

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B. burgdorferi IgG, IgM by Western Blot

Q: Can a positive Western blot indicate active infection or only past exposure?

A positive IgG Western blot indicates antibody presence, which persists for years after treatment, so it cannot distinguish active infection from past exposure. Diagnosis of active Lyme disease requires compatible clinical features and epidemiology, not serology alone.

The Borrelia burgdorferi IgG and IgM Western Blot is the second-tier confirmatory serological test in the CDC two-tier algorithm for Lyme disease, detecting antibodies to specific spirochaetal proteins by band pattern. IgG positivity (≥5 of 10 CDC bands) confirms exposure and supports late or disseminated disease;

Biomarkers

Blood (serum)

Sample

5–10 business days

Turnaround

Fasting

What is the Lyme Western Blot test?

The Borrelia burgdorferi IgG and IgM Western Blot is a confirmatory serological test that detects antibodies to specific proteins of the Lyme disease spirochaete. It is the standard second tier of the CDC-recommended two-tier testing algorithm, ordered only after a positive or equivocal enzyme immunoassay or chemiluminescence immunoassay to reduce false positives. Western blot separates Borrelia antigens by molecular weight, revealing a band pattern that reflects the host's immune response to distinct spirochaetal proteins; the number and identity of reactive bands determine whether the test is positive, negative, or indeterminate according to validated interpretive criteria. Because serology depends on antibody formation, it is insensitive in the first two to three weeks of infection — a negative Western blot does not exclude early localised Lyme disease when erythema migrans is present. Conversely, antibodies persist for years after successful treatment, so a positive IgG blot cannot distinguish active infection from past exposure. The test is thus most useful for confirming suspected early disseminated or late disease, supporting a clinical diagnosis, and excluding Lyme in patients with non-specific symptoms and low pre-test probability.

What does the Lyme Western Blot test measure?

Bb IgG WB(Borrelia burgdorferi IgG by Western Blot)

Range: ≥5 of 10 bands (CDC criteria: 18, 21, 28, 30, 39, 41, 45, 58, 66, 93 kDa) for positive; some laboratories report expanded or modified band sets.Optimal: Not applicable; this is a qualitative serological test. The presence or absence of specific bands is read against validated interpretive criteria rather than a continuous reference range.Qualitative band pattern

IgG antibodies to Borrelia burgdorferi sensu lato surface and flagellar proteins appear weeks to months after tick-borne infection and persist for years, even after treatment. Western blot separates serum immunoglobulins by protein molecular weight, transferring them to a membrane that is incubated with Borrelia lysate; reactivity to specific kilodalton bands reflects antibody recognition of distinct spirochaete antigens. The band pattern — not the absolute number of reactive bands alone — determines interpretation, and IgG responses are most reliable in late disseminated or chronic Lyme disease.

IgG Western blot is the second-tier confirmatory test in the CDC two-tier algorithm for Lyme disease, ordered when an enzyme immunoassay or chemiluminescence assay is positive or equivocal. It is particularly informative in late or persistent disease, where IgG dominates and IgM may have waned or never appeared. Expanded band criteria used by some specialty laboratories may increase sensitivity but reduce specificity, so interpretation must account for the band set and criteria applied.

Bb IgM WB(Borrelia burgdorferi IgM by Western Blot)

Range: ≥2 of 3 bands (CDC criteria: 23, 39, 41 kDa) for positive; laboratories may report additional bands for clinical context.Optimal: Not applicable; this is a qualitative serological test. Reactivity is interpreted against validated band criteria and symptom duration, not a continuous scale.Qualitative band pattern

IgM antibodies to Borrelia burgdorferi surface antigens rise within weeks of infection and typically wane by three to six months, though they can persist. The IgM Western blot identifies early adaptive humoral responses to a narrow set of immunodominant proteins, primarily the 41-kDa flagellin, 39-kDa BmpA, and 23-kDa OspC. Because IgM responses can cross-react with other spirochaetes and because isolated IgM positivity is common in false-positive results, IgM Western blot is interpreted only in the context of early disease (symptom onset within 30 days) and never used for late or chronic presentations.

IgM Western blot confirms early Lyme disease when the first-tier assay is reactive and symptoms are recent. It should not be ordered in isolation or in patients with prolonged symptoms, because late false-positive IgM is common and clinically misleading. The 41-kDa band is highly sensitive but non-specific, appearing in other spirochaetal infections and sometimes in healthy controls, so a positive IgM blot requires two of the three CDC bands and appropriate clinical context.

Why is the Lyme Western Blot test ordered?

Confirmation of Lyme disease in patients with a positive or equivocal first-tier enzyme immunoassay and compatible clinical features (erythema migrans, Bell's palsy, Lyme arthritis, or carditis)
Evaluation of early disseminated or late Lyme disease when initial serology is indeterminate and symptoms persist or progress
Exclusion of Lyme disease in patients with chronic fatigue, arthralgia, or neurological complaints and intermediate pre-test probability, to interpret an equivocal screening test
Investigation of suspected Lyme arthritis in patients with inflammatory monoarthritis or oligoarthritis of large joints, particularly the knee
Work-up of neurological manifestations compatible with neuroborreliosis (facial palsy, lymphocytic meningitis, radiculopathy) in endemic regions, alongside cerebrospinal fluid testing when appropriate
Assessment of patients with suspected post-treatment Lyme disease syndrome, to document prior infection when earlier serological confirmation was not obtained
Re-evaluation of discordant or ambiguous first-tier results when clinical suspicion remains, though repeat testing within four weeks of a negative result is not recommended unless new exposure or symptom evolution has occurred

Sample collection and turnaround

Sample type

Blood (serum)

Fasting required

Collection method

Venipuncture at patient service centre

Turnaround

5–10 business days

Collection notes

Phlebotomy required; timing relative to symptom onset is critical for interpretation — if symptoms began within the past two weeks, repeat serology in four to six weeks if initial results are negative or equivocal. Note any recent or current antibiotic therapy and prior Lyme disease or tick exposure on the requisition. Immunosciences Lab performs the Western blot; specimen handling and shipping requirements should be confirmed with the laboratory.

Specimen requirements

Minimum volume and separator-tube requirements should be confirmed with Immunosciences Lab; Western blot typically requires ≥1 mL serum. Specimens are generally stable refrigerated for several days; confirm acceptable transport and storage conditions with the performing laboratory.

What can affect Lyme Western Blot results?

reducesTiming relative to symptom onset

Antibody responses require two to four weeks to develop, so Western blot is insensitive in the first weeks of infection; repeat testing four to six weeks later is needed if early disease is strongly suspected and initial serology is negative.

reducesEarly antibiotic therapy

Prompt treatment of erythema migrans may blunt or prevent seroconversion, resulting in a persistently negative or weakly positive Western blot despite true infection; diagnosis rests on clinical recognition of the rash.

elevatesCross-reactivity with other spirochaetes

Antibodies to Treponema pallidum (syphilis), relapsing-fever Borrelia, and leptospirosis can produce bands, particularly the non-specific 41-kDa flagellin; clinical and epidemiological context and additional serological testing (e.g., syphilis serology) help resolve ambiguity.

variableAutoimmune and connective-tissue disease

Patients with systemic lupus erythematosus, rheumatoid arthritis, and other autoimmune conditions occasionally show non-specific bands, leading to false-positive or indeterminate patterns; interpret alongside disease-specific autoantibodies.

elevatesPersistent antibodies after treatment

IgG antibodies persist for years, so a positive IgG Western blot can reflect past treated infection rather than active disease; serial titre changes are not reliable for assessing treatment response or reinfection.

variableLaboratory-specific band criteria

Specialty laboratories may report expanded band sets beyond CDC criteria, increasing sensitivity but reducing specificity; practitioners must know which interpretive criteria were applied and recognise that expanded criteria are not validated for routine use.

What do Lyme Western Blot results mean?

Elevated

Positive IgG Western blot (≥5 of 10 CDC bands) confirms exposure to B. burgdorferi and supports a diagnosis of Lyme disease when clinical features and epidemiology are compatible; it is the definitive serological marker of late disseminated or chronic Lyme disease. Positive IgM Western blot (≥2 of 3 CDC bands) is relevant only in early disease (symptom onset ≤30 days) and must be interpreted with caution because late false-positive IgM is common; IgM positivity in prolonged or non-specific illness is usually a false positive and should not prompt treatment.

Normal

Negative IgG and IgM Western blot in the appropriate clinical and temporal context argues strongly against Lyme disease, though it does not exclude very early localised infection (first two to three weeks) or infection in an immunocompromised host. If erythema migrans is present, treatment should proceed regardless of serology, and repeat testing in four to six weeks may capture delayed seroconversion.

Reduced

Not applicable; Western blot is a qualitative presence/absence test rather than a quantitative assay with low values.

Note: Western blot is the second tier of a two-tier algorithm and should never be ordered without a positive or equivocal first-tier assay, because the pre-test probability shapes predictive value. IgM results are clinically valid only in early disease and should be disregarded in patients with symptoms for more than 30 days. A positive test indicates antibody presence, not active infection, so it cannot be used to diagnose reinfection, monitor treatment response, or confirm cure. Expanded or modified band criteria may be reported by specialty laboratories; practitioners must understand which criteria were applied and that non-CDC criteria are not universally accepted.

Frequently asked questions

The ELISA or chemiluminescence assay is the first-tier screening test, designed to be sensitive. The Western blot is the second-tier confirmatory test, ordered only when the ELISA is positive or equivocal, and is more specific because it identifies antibodies to individual Borrelia proteins by band pattern.

How to access the Lyme Western Blot test

The Lyme Western Blot reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.

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About this page

Published: October 7, 2026

Last reviewed: October 7, 2026

References:

Wormser GP, et al. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. (2006)
Centers for Disease Control and Prevention. Recommendations for test performance and interpretation from the Second National Conference on Serologic Diagnosis of Lyme Disease. MMWR. (1995)
Steere AC, et al. Lyme borreliosis. Nat Rev Dis Primers. (2016)
Lantos PM, et al. Clinical practice guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 guidelines for the prevention, diagnosis and treatment of Lyme disease. Clin Infect Dis. (2021)
Branda JA, Steere AC. Laboratory diagnosis of Lyme borreliosis. Clin Microbiol Rev. (2021)

This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.