Guideline Recommendations for HSV‑1 and HSV‑2 Diagnostic Testing

Direct Testing from Active Lesions

For patients presenting with genital ulcers or lesions, perform HSV nucleic acid amplification testing (NAAT/PCR) that distinguishes HSV‑1 from HSV‑2; this is the gold‑standard diagnostic method for active infection. 1
NAAT/PCR assays are preferred over viral culture because they achieve >90 % sensitivity and specificity, whereas culture sensitivity declines as lesions begin to heal. 1
Molecular assays should not be ordered when no visible lesions are present, because intermittent viral shedding renders the test insensitive. 1
If only viral culture is available (e.g., due to cost or laboratory limitations), it may be used, but clinicians must recognize its lower sensitivity and consider follow‑up serology when results are negative and clinical suspicion remains high. 1
Direct immunofluorescence assays and Tzanck smears are not recommended because they lack adequate sensitivity. 1

Use type‑specific serologic assays that detect antibodies to HSV glycoprotein G‑1 (HSV‑1) and G‑2 (HSV‑2) via enzyme immunoassay (EIA) or chemiluminescent immunoassay (CLIA); be aware of their significant limitations. 1

HSV‑1 serologic assays have approximately 70 % sensitivity, meaning about 30 % of truly infected individuals may receive a false‑negative result. 1
HSV‑2 serologic assays have higher sensitivity (~92 %) but still miss roughly 8 % of true infections. 1
Specificity for HSV‑2 serology is low at low index values (1.1–2.9), with specificity ≈ 39.8 %; specificity improves to ≈ 78.6 % when index values are ≥ 3.0, yet remains suboptimal. 1
Individuals with prior HSV‑1 infection are more prone to false‑positive HSV‑2 results when the HSV‑2 index value is low (1.1–2.9). 1

Serology should be performed ≥ 12 weeks after the suspected exposure; testing earlier may yield false‑negative results because antibodies may not yet be detectable. 1

Patients with recurrent genital symptoms when active lesions are unavailable for NAAT/PCR. 1
Partners of individuals known to be HSV‑positive. 1
High‑risk groups (e.g., persons living with HIV, individuals with multiple sexual partners). 1
Pregnant women when clinically indicated. 1
Patients with an uncertain clinical diagnosis who present without active lesions. 1

Do not tell patients that a negative serology definitively excludes prior HSV exposure; false‑negative rates are substantial (≈ 30 % for HSV‑1, ≈ 8 % for HSV‑2). 1
Do not use serology to diagnose active genital ulcers; always obtain NAAT/PCR directly from the lesion. 1
Western blot/immunoblot remains the confirmatory gold standard but is generally limited to research laboratories. 1
When HSV‑2 serology yields a low index value (1.1–2.9), confirmatory testing should be considered because of poor specificity in this range. 1

Commercial HSV‑1 antibody assays have a sensitivity of approximately 70 % (≈30 % false‑negative rate) in infected individuals. 2
HSV‑2 serologic assays are more sensitive (≈92 %) but still miss about 8 % of true infections. 3

Detectable antibodies may not appear until up to 12 weeks after HSV exposure; testing earlier can yield false‑negative results. 4
Serologic testing performed before 12 weeks post‑exposure should be deferred; repeat testing is recommended no sooner than 12 weeks after the suspected exposure. 4

When exposure occurred within 12 weeks or clinical suspicion remains high, a negative serology is unreliable; repeat testing after 12 weeks or direct lesion testing (NAAT/PCR) is advised. 2
A negative HSV‑1 result is especially unreliable because of the assay’s low sensitivity; clinicians should interpret such results with caution. 5
Negative serology obtained >12 weeks after the last possible exposure is more trustworthy, particularly for HSV‑2 testing in patients without concurrent HSV‑1 infection. 2
Absence of any clinical history suggestive of HSV infection increases confidence in a negative result. 6

The widely used HerpeSelect and similar EIA/CLIA assays exhibit the sensitivity limitations described above. 3
Western blot/immunoblot remains the gold‑standard confirmatory test but is generally limited to research laboratories. 5
Cross‑reactivity can cause false‑positive HSV‑2 results in patients with HSV‑1 infection, though it does not affect the false‑negative rate for true infections. 3

In patients with active lesions suspicious for HSV, a negative serology does not exclude infection; lesion sampling for NAAT/PCR is the preferred diagnostic approach. 7
Serologic testing should be reserved for situations where no active lesions are present. 6

Clinicians should not tell patients that a negative HSV serology definitively proves lack of prior exposure; for HSV‑1 the sensitivity is only about 70 % (≈30 % false‑negatives) and for HSV‑2 about 92 % (≈8 % false‑negatives). 2