What is the initial step in testing for Lyme disease?

Testing for Lyme Disease

The initial step in testing for Lyme disease depends critically on clinical presentation: patients with erythema migrans (EM) in endemic areas should be diagnosed clinically without laboratory testing, while all other suspected cases require two-tiered serologic testing starting with an enzyme immunoassay (EIA/ELISA) or immunofluorescence assay (IFA). 1

Clinical Diagnosis Without Testing

For patients presenting with erythema migrans (a gradually expanding annular lesion >5 cm in diameter) who live in or have recently traveled to Lyme-endemic areas (northeast and upper midwest United States), laboratory testing is not necessary and diagnosis should be made clinically. 1

• Approximately 70-80% of Lyme disease patients present with EM 1
• Clinical diagnosis in this scenario avoids the window period problem where antibody testing has poor sensitivity (only 30-40%) during early infection 1
• Accompanying symptoms may include fever, lymphadenopathy, myalgias, or arthralgias 1

Two-Tiered Serologic Testing Algorithm

For all patients without EM or with suspected disseminated disease, the standard of care 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

First-Tier Testing

• Begin with an enzyme immunoassay (EIA/ELISA) or immunofluorescence assay (IFA) measuring IgM and IgG antibodies to Borrelia burgdorferi. 1
• EIA is preferred over IFA because it is more easily automated and provides quantitative values 1
• Whole-cell sonicate preparations are most commonly used, though newer C6 peptide EIAs offer improved specificity with similar sensitivity 1
• Only proceed to second-tier testing if the first-tier result is positive or equivocal 1

Second-Tier Testing

• If first-tier testing is positive or equivocal, perform Western immunoblot (IgM and/or IgG depending on symptom duration). 1
• For symptoms lasting <30 days: perform both IgM and IgG Western immunoblots 1
• For symptoms lasting ≥30 days: perform only IgG Western immunoblot (IgM alone should not be used after 30 days due to false positives) 1
• This two-step approach increases specificity to >98%, reducing false-positives from the first-tier test alone 1

Test Performance Characteristics

Two-tiered testing has sensitivity of 70-100% and specificity >95% for disseminated Lyme disease, but sensitivity drops to only 30-40% during early localized infection. 1

• For early disease with EM in acute phase: sensitivity is only 40% 1
• For early disease with EM in convalescent phase (3-4 weeks later): sensitivity improves to 61% 1
• For disseminated disease (neuritis, carditis, arthritis): sensitivity reaches 88-100% 1
• Specificity remains >95% across all disease stages 1

Critical Pretest Probability 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

• In low-incidence states without recent travel to endemic areas, positive predictive value is only 10% 1
• Only 0.7% of patients in non-endemic areas with arthritis, cranial neuropathies, or meningitis actually have Lyme disease 1
• Do not order serologic testing for patients without exposure to endemic areas (northeast and upper midwest US), as positive results provide little diagnostic value 1

Common Pitfalls to Avoid

Never order Western immunoblot without first performing EIA/IFA—this dramatically increases false-positive rates. 1

• Alternative laboratories using unvalidated interpretation criteria show false-positive rates as high as 58% in healthy controls 1
• Avoid urine antigen tests and CD57 tests, which lack validation 1
• Do not retest patients after treatment—antibodies persist for months to years after successful treatment and do not indicate active infection 2
• Persistent antibodies should not be confused with persistent infection 2
• Clinical response, not serologic findings, should determine treatment success 2

When Convalescent Testing Is Needed

For patients with suspected early Lyme disease who test negative in the acute phase, obtain convalescent serology 3-4 weeks later. 1

• Sensitivity improves from approximately 40% to 61% between acute and convalescent phases for EM patients 1
• This accounts for the antibody window period during early infection 1