Testing for HSV-2
For active genital lesions, use nucleic acid amplification testing (NAAT/PCR) from the lesion as your first-line diagnostic test; for asymptomatic individuals or when no lesions are present, use type-specific serological testing with glycoprotein G-based assays on venous blood. 1, 2
Testing Strategy Based on Clinical Presentation
When Active Genital Lesions Are Present
NAAT/PCR is the preferred diagnostic test for detecting HSV-2 from genital ulcers or lesions, with sensitivity and specificity exceeding 90% for most FDA-approved assays. 1 This method offers 11-71% superior sensitivity compared to viral culture and allows simultaneous detection and typing of HSV-1 and HSV-2 in a single reaction. 3
Optimal sampling technique:
- Collect fluid from intact vesicles or swab the base of ulcers 3
- For male patients, obtain urethral swabs 3
- For female patients, use cervical/urethral swabs 3
- NAAT allows less strict sample transportation conditions compared to viral culture 3
Important caveat: Do not obtain HSV molecular assays in the absence of genital ulcers—due to intermittent viral shedding, swabs from intact skin are not sensitive and will yield false-negative results. 1
If NAAT is unavailable: Viral culture is acceptable as a second-choice diagnostic method, though it has significantly lower sensitivity. 1, 3 If HSV is suspected and culture results are negative, follow up with serologic testing to rule out HSV-2 infection. 1
Avoid these tests: Direct immunofluorescence assay and Tzanck smear lack adequate sensitivity and should not be used for diagnosis. 1, 3
When No Lesions Are Present (Asymptomatic Testing)
Use type-specific serological testing with glycoprotein G-based enzyme immunoassay (EIA) or chemiluminescent immunoassay (CLIA) on venous blood samples. 2 These tests have approximately 97% sensitivity and 98% specificity for detecting HSV-2 antibodies. 2
Do not use NAAT for screening asymptomatic individuals—this test is only appropriate when active lesions are present. 2
Interpreting Serological Test Results
Understanding Index Values
The specificity of HSV-2 serological tests is highly dependent on the index value reported:
- Index value <0.9: Negative 1
- Index value 0.9-1.1: Indeterminate 1
- Index value 1.1-2.9: Positive, but specificity is only 39.8% 1, 4
- Index value ≥3.0: Positive with improved specificity of 78.6% 1, 4
Critical Pitfall: False-Positive Results
For low positive results (index value <3.0), always confirm with a second test using a different glycoprotein G antigen. 2, 4 False-positive HSV-2 results are particularly common in individuals with HSV-1 infection, especially at low index values. 1, 4 Using the Biokit HSV-2 rapid assay as confirmatory testing improves specificity from 93.2% to 98.7% compared to Western blot. 4
Western blot/immunoblot is the gold standard for HSV serologic testing but has limited availability. 1, 2, 4
Window Period Considerations
A negative result within 12 weeks of potential exposure may represent the "window period" before antibodies develop. 2, 4 HSV-2 IgG antibodies develop within several weeks after infection. 2, 4 If recent acquisition is suspected, repeat testing after 12 weeks. 2, 4
The sensitivity of HSV-2 serologic testing is high at 92%, but false-negatives can occur during this early window period. 1
What a Positive Result Means
A positive HSV-2 IgG antibody test indicates past exposure and ongoing latent infection with HSV-2, with antibodies persisting indefinitely. 2, 4 The test cannot distinguish between recent and long-standing infections. 2, 4
Do not use IgM testing for screening—approximately one-third of patients with recurrent genital herpes caused by HSV-2 have IgM responses, making it unreliable for distinguishing primary from recurrent infection. 2
Who Should Be Tested Serologically
Recommended populations for type-specific HSV-2 serology: 2, 3
- 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
Widespread screening of the general asymptomatic population is not recommended. 2, 3 The US Preventive Services Task Force recommends against screening for HSV-2 infection among asymptomatic adolescents and adults. 3
Why HSV-1 vs HSV-2 Typing Matters
Always use assays that differentiate between HSV-1 and HSV-2 to provide accurate prognostic information. 1, 3 HSV-2 causes more frequent recurrences and subclinical viral shedding compared to HSV-1 genital infections. 4, 3 Up to 50% of first-episode genital herpes cases are caused by HSV-1, but recurrences are less frequent with genital HSV-1. 3
Important limitation: HSV-1 serologic assays lack sensitivity (only 70.2% in one study), which can result in false-negative diagnoses. 1 HSV-1 IgG detection has poor specificity and positive predictive value for diagnosing genital ulcer disease and may not be clinically useful in this context. 5