What laboratory tests should be ordered for a patient with suspected Lyme disease?

Laboratory Testing for Suspected Lyme Disease

Order two-tiered serologic testing consisting of an enzyme immunoassay (EIA) or immunofluorescence assay (IFA) as the first tier, followed by reflex Western immunoblot only if the first test is positive or equivocal. 1, 2

Critical Exception: Do Not Test Patients with Erythema Migrans

• If the patient has erythema migrans (expanding annular lesion >5 cm) and lives in or traveled to an endemic area, diagnose clinically without any laboratory testing and treat immediately. 1, 2
• Approximately 70-80% of Lyme disease patients present with erythema migrans, and serologic testing has only 30-40% sensitivity during this early stage, making it clinically useless and potentially misleading. 1, 2
• Accompanying symptoms to support clinical diagnosis include fever, lymphadenopathy, myalgias, or arthralgias. 1

Two-Tiered Testing Algorithm for Disseminated Disease

First-Tier Test

• Order an EIA (most common) or IFA to detect total antibody response (IgM and IgG) to Borrelia burgdorferi antigens. 1
• Most U.S. laboratories use whole-cell sonicate EIA, though newer C6 peptide or VlsE antigen-based EIAs offer similar sensitivity with higher specificity. 1
• The first-tier test is highly sensitive but has suboptimal specificity when used alone due to cross-reactivity with other pathogens. 1

Second-Tier Test (Reflex Only)

• Perform Western immunoblot only if the first-tier EIA/IFA is positive or equivocal—never order Western blot as a standalone test. 1, 2
• For patients presenting within 1 month of symptom onset, test for both IgM and IgG antibodies. 1
• For patients presenting >1 month after symptom onset, test only for IgG antibodies, as IgM can produce false-positives at this stage. 1
• This two-tiered approach increases specificity to >98% and reduces false-positive results. 1

Test Performance by Disease Stage

Early Localized Disease (Erythema Migrans)

• Sensitivity in acute phase: only 40% 1, 2
• Sensitivity in convalescent phase (3-4 weeks later): 61% 1, 2
• This poor early sensitivity is why clinical diagnosis without testing is recommended for erythema migrans. 2

Early Disseminated Disease (Neuritis, Carditis)

• Sensitivity: 88-100% 1, 2
• Specificity: >95% 1, 2

Late Disseminated Disease (Arthritis)

• Sensitivity: 96-100% 1, 2
• Specificity: >95% 1, 2

Additional Testing for Specific Manifestations

Neuroborreliosis

• Obtain cerebrospinal fluid (CSF) and concurrent serum sample for determination of intrathecal antibody production, cell counts/differentials, and protein content. 1
• Laboratory confirmation is achieved by demonstrating borrelia-specific intrathecal antibody production. 1
• CSF PCR can be performed but has only 20% detection rate. 1

Lyme Arthritis

• Order PCR testing of synovial fluid or, preferably, synovial biopsy specimen. 1
• Synovial fluid and serum display roughly equivalent antibody titers due to high protein permeability of the synovium. 1

Skin Biopsy (Rarely Needed)

• Skin biopsy specimens from the expanding border of erythema migrans (within 4 mm) can be cultured with up to 86% success rate in untreated patients. 1
• This is rarely necessary in clinical practice given the high clinical diagnostic accuracy. 1

Critical Pretest Probability Assessment

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

• In non-endemic states without recent travel to endemic areas, positive predictive value is only 10%. 2
• Only 0.7% of patients in non-endemic areas with arthritis, cranial neuropathies, or meningitis actually have Lyme disease. 2
• Endemic areas include the northeast and upper midwest United States. 1

Common Pitfalls to Avoid

• Never order Western immunoblot without first performing EIA/IFA—this dramatically increases false-positive rates. 2
• Never order urine antigen tests or CD57 tests—these lack validation and are not recommended. 2
• Never retest patients after treatment—antibodies persist for months to years after successful treatment and do not indicate active infection. 2
• Never rely on negative acute-phase serology to exclude Lyme disease—antibodies are typically absent during the first 3 weeks of illness. 2, 3
• Never order imaging as a screening tool for Lyme disease—this leads to incidental findings, patient anxiety, unnecessary costs, and radiation exposure without diagnostic benefit. 4

Supportive Laboratory Tests (Not Lyme-Specific)

If considering other tick-borne illnesses in the differential diagnosis:

• Order complete blood count (CBC) with differential to assess for thrombocytopenia and leukopenia characteristic of ehrlichiosis/anaplasmosis. 3
• Order comprehensive metabolic panel to assess liver function, as hepatic abnormalities occur in 50-75% of ehrlichiosis and anaplasmosis cases. 3
• Consider PCR testing for Anaplasma phagocytophilum and Ehrlichia chaffeensis if clinical suspicion exists. 3