HSV-2 Laboratory Testing
For active genital lesions, nucleic acid amplification testing (NAAT/PCR) from the lesion is the first-line diagnostic test, while type-specific serological testing using glycoprotein G-based assays should be used when no lesions are present or for screening high-risk populations. 1, 2
Diagnostic Approach Based on Clinical Presentation
Active Genital Lesions
- NAAT/PCR is the preferred test for detecting HSV-2 from genital ulcers or lesions, offering 11-71% superior sensitivity compared to viral culture. 1, 2
- Optimal sampling technique includes collecting fluid from intact vesicles or swabbing the base of ulcers. 2
- If NAAT is unavailable, viral culture is acceptable as a second-choice method, though it has significantly lower sensitivity. 1
- HSV direct immunofluorescence assay and Tzanck smear are not recommended due to lack of sensitivity. 1
- Type-specific testing (HSV-1 vs HSV-2) should always be performed to provide accurate prognostic information, as HSV-2 causes more frequent recurrences and subclinical viral shedding compared to HSV-1 genital infections. 1, 3
No Active Lesions Present
- Type-specific serological testing with glycoprotein G-based assays on venous blood samples is recommended. 4, 2
- NAAT/PCR should NOT be obtained in the absence of genital ulcers due to the intermittent nature of genital HSV shedding, which would result in poor sensitivity. 1
Serological Testing: Critical Interpretation Guidelines
Understanding Index Values
The index value is crucial for interpreting HSV-2 serological results: 1
- <0.9: Negative
- 0.9-1.1: Indeterminate
- 1.1-2.9: Positive but with only 39.8% specificity
- ≥3.0: Positive with 78.6% specificity
Confirmatory Testing Strategy
- For index values <3.0, confirmation with a second test using a different glycoprotein G antigen is strongly recommended to avoid false-positive results. 1, 4
- Using the Biokit HSV-2 rapid assay as a confirmatory test improves specificity from 93.2% to 98.7% and positive predictive value from 80.5% to 95.6%. 1
- If Biokit is unavailable, Western blot can be used as a confirmatory test, though access may be limited. 1
- Index values ≥3.0 may be sufficient for diagnosis without further confirmatory testing, though false positives have been described even at values >3.5. 1
Common Pitfalls to Avoid
- False-positives are more common in individuals with HSV-1 infection, especially with low index values. 1, 4
- The window period may be up to 12 weeks after exposure—a negative result within this timeframe should be repeated after 12 weeks if recent acquisition is suspected. 1, 4, 2
- HSV-1 serological assays lack sensitivity (only 70.2% in one study), which can result in false-negative diagnoses. 1
- IgM testing is NOT recommended for screening, as approximately one-third of patients with recurrent genital herpes caused by HSV-2 have IgM responses, making it a poor indicator of recent infection. 1, 4
Who Should Be Tested Serologically
Recommended Populations
Type-specific HSV-2 serology should be used for: 1, 4, 2
- Pregnant women at risk of acquiring HSV infection close to delivery
- Men who have sex with men
- People who are HIV positive
- Sexual partners of individuals with known genital herpes
- Asymptomatic individuals with atypical presentations or no lesions
Not Recommended
- Widespread screening for HSV-2 antibodies in the general asymptomatic population is discouraged due to the potential for false-positive results and limited clinical utility. 1, 4, 2
Clinical Significance of Results
Positive HSV-2 Serology
- Indicates past exposure and ongoing latent infection with HSV-2, with antibodies persisting indefinitely. 1, 2
- The test cannot distinguish between recent and long-standing infections. 4
- Patients should be counseled about the natural history of disease, potential for recurrent episodes, asymptomatic viral shedding, and sexual transmission risk. 4, 2
Treatment Considerations
- Treatment options include episodic therapy for outbreaks or suppressive therapy to reduce recurrences and transmission risk. 4
- Acyclovir, valacyclovir, and famciclovir are FDA-approved antivirals with demonstrated activity against HSV-2. 5, 6, 7