What are the laboratory tests and diagnostic approach for a patient suspected of having Lyme disease, particularly in endemic areas with potential exposure to ticks?

Laboratory Diagnosis of Lyme Disease

Clinical Diagnosis Without Laboratory Testing

Patients presenting with erythema migrans (EM) in endemic areas should be diagnosed clinically and treated immediately without laboratory testing. 1, 2 This approach is critical because:

• Approximately 70-80% of Lyme disease patients present with EM, making it the most common manifestation 1, 2
• Serologic testing has poor sensitivity (only 30-40%) during early localized infection due to the antibody window period 1, 2
• EM is defined as a gradually expanding annular lesion >5 cm in diameter 1
• Waiting for laboratory confirmation delays treatment and risks progression to disseminated disease 1, 2

Two-Tiered Serologic Testing Algorithm

For all suspected Lyme disease cases without EM, the standard diagnostic approach is two-tiered serologic testing: first-tier EIA or IFA, followed by reflex Western immunoblot only if the first test is positive or equivocal. 1, 3, 2

First-Tier Testing

• Order enzyme-linked immunoassay (EIA/ELISA) or immunofluorescence assay (IFA) as the initial screening test 1, 3
• EIA is considered more reliable and accurate than IFA, but IFA may be used if EIA is unavailable 1
• Never order Western immunoblot without first performing EIA/IFA—this dramatically increases false-positive rates 2

Second-Tier Testing (Reflex Only)

• Western immunoblot (both IgM and IgG) should only be performed if the first-tier test is positive or equivocal 1, 3
• For disease duration <6-8 weeks: IgM Western blot is valid and requires ≥2 of 3 specific bands (plus positive/equivocal EIA) 4, 3
• For disease duration >6-8 weeks: Only IgG Western blot is clinically interpretable, requiring ≥5 of 10 specific bands 4, 3
• An IgG-negative, IgM-positive result obtained more than one month after symptom onset likely represents a false-positive IgM result 4

Test Performance Characteristics

The sensitivity and specificity of two-tiered testing varies dramatically by disease stage 1, 2:

• Early localized disease with EM: Sensitivity only 40% in acute phase, improving to 61% at 3-4 weeks (convalescent phase) 2
• Disseminated disease (neuritis, carditis, arthritis): Sensitivity 88-100% 3, 2
• Specificity: >95% across all disease stages 1, 2

Pretest Probability and Geographic Considerations

Geographic exposure history is the most crucial factor determining whether to test—even highly specific tests produce false-positives when pretest probability is low. 1, 2

Endemic Area Considerations

• Cases occur primarily in the northeastern and upper midwest United States 1
• In endemic areas, Lyme disease can cause facial paralysis in up to 25% of cases 1
• For patients in endemic areas or with recent travel to endemic areas, testing is appropriate when clinical suspicion exists 1

Non-Endemic Area Pitfalls

• In low-incidence states without recent travel to endemic areas, positive predictive value is only 10% 1, 2
• Only 0.7% of patients in non-endemic areas with arthritis, cranial neuropathies, or meningitis actually have Lyme disease 1, 2
• False-positive results are more likely than true-positive results in low pretest probability patients 1
• Even EM-like lesions can be caused by other conditions such as Southern tick-associated rash illness (STARI) in the southeastern United States 1

Specific Clinical Scenarios Requiring Testing

Disseminated Disease Manifestations

Order testing for patients with objective signs of disseminated disease, as these have high predictive value and test sensitivity: 4, 3

• Acute neurologic manifestations: meningitis, painful radiculoneuritis, mononeuropathy multiplex, acute cranial neuropathies (especially facial palsy), or spinal cord inflammation 3
• Cardiac manifestations: acute myocarditis/pericarditis with dyspnea, palpitations, chest pain, syncope, or conduction abnormalities 3
• Recurrent large-joint arthritis (hallmark of late disseminated disease) 1
• Multiple EM skin lesions 1

Neuroborreliosis

• Order CSF analysis with cell count, differential, protein, and Lyme antibody index, along with concurrent serum sample for comparison 3
• CSF testing is essential for suspected CNS involvement 3

Lyme Arthritis

• Consider synovial fluid or synovial biopsy for Lyme PCR in addition to serology 3

Critical Testing Pitfalls to Avoid

Do NOT Order Testing In These Situations:

• At the time of a tick bite: Antibodies are unlikely to be detectable and results would be misleading 3
• For nonspecific symptoms alone: Fatigue, headache, or myalgias have poor predictive value without objective findings 4
• For routine screening in low-risk patients: Typical ALS, relapsing-remitting MS, Parkinson's disease, dementia, new-onset seizures, psychiatric illness, or developmental/behavioral disorders 3
• After treatment completion: Antibodies persist for months to years after successful treatment and do not indicate active infection 4, 3, 2

Unvalidated Tests to Avoid:

• Never order urine antigen tests or CD57 tests—these lack validation and are not recommended by any guideline 3, 2
• Avoid alternative laboratories using non-standard interpretation criteria or laboratory-developed tests not subject to FDA regulations 1

Interpretation Caveats

Antibody Persistence

• The absence of IgG antibodies in a patient with a history of Lyme disease makes a new active infection unlikely 4
• Do not confuse antibody persistence with active infection—antibodies can persist for months to years after successful treatment 4
• Never retest after treatment, as positive serology does not indicate treatment failure or reinfection 3, 2

Marginally Positive Results

• IgM values barely above the cutoff increase the likelihood of laboratory variation or cross-reactivity rather than true infection 4
• Do not treat based solely on a marginally positive IgM in the absence of clinical findings 4

Alternative Diagnostic Modalities (Limited Use)

Direct detection methods have limited clinical utility 1:

• PCR or culture: Challenging because spirochetes only transiently enter the bloodstream in small numbers 1
• Synovial fluid PCR: May be useful for suspected Lyme arthritis 3
• Most diagnostic test development has focused on antibody detection due to limitations of direct detection 1