Best Way to Test for HSV
For patients with active genital lesions, nucleic acid amplification tests (NAAT/PCR) are the first-line diagnostic test due to superior sensitivity (11-71% better than viral culture) and the ability to simultaneously detect and differentiate HSV-1 from HSV-2. 1, 2
Testing Strategy Based on Clinical Presentation
Active Lesions Present
- Obtain NAAT/PCR from lesion swabs as the preferred diagnostic method, sampling fluid from intact vesicles or the base of ulcers for optimal yield 1, 2
- NAAT/PCR demonstrates >90% sensitivity and specificity, with most FDA-approved assays performing at this level 1
- Real-time PCR allows detection and typing in a single reaction tube, completed in approximately 2 hours 1
If NAAT is unavailable due to cost or laboratory limitations:
- Viral culture is acceptable as a second-line option, though sensitivity drops significantly as lesions heal (>90% for vesicular lesions, 70% for ulcerative lesions, only 27% at crusting stage) 1
- Culture requires transport on ice and processing within 24 hours, with results taking 24-72 hours (up to 5 days) 1, 2
No Active Lesions Present
- Use type-specific serologic testing with glycoprotein G-based assays for diagnosis when lesions are absent 1, 2
- HSV-2 serology has high sensitivity (92%) but specificity issues exist, particularly with low index values 1
- Do NOT obtain HSV molecular assays in the absence of genital ulcers - intermittent viral shedding makes this approach insensitive 1
Critical Interpretation Guidelines for Serology
HSV-2 Antibody Testing
- Index values <0.9 are negative, 0.9-1.1 indeterminate, >1.1 positive per manufacturer labeling 1
- However, specificity is problematic: index values 1.1-2.9 have only 39.8% specificity; values ≥3.0 have 78.6% specificity 1
- For low positive results (index <3.0), confirm with a second test using different glycoprotein G antigen 3
- Patients with HSV-1 infection are more likely to have false-positive HSV-2 results with low index values 1
HSV-1 Antibody Testing
- Current EIA/CLIA assays lack sensitivity (only 70.2% in one study), resulting in frequent false-negatives 1
- Western blot/immunoblot is the gold standard but has limited availability 1, 3
Important Clinical Pitfalls to Avoid
Window Period Issues
- Negative serology within 12 weeks of potential exposure may represent the window period - repeat testing after 12 weeks if recent acquisition suspected 1, 3
- Antibodies develop within several weeks after infection 3
Tests NOT Recommended
- Direct immunofluorescence assay and Tzanck smear lack sensitivity and should not be used 1, 2
- HSV-specific IgM testing is unreliable - approximately one-third of patients with recurrent HSV-2 have IgM responses, making it a poor indicator of recent infection 1, 3
Site-Specific Sampling Recommendations
- Vesicular rash on skin/mucous membranes: NAAT or antigen detection 1
- Male urethra: NAAT or antigen detection 1
- Female cervix/urethra: NAAT or antigen detection 1
- Urine (both sexes): NAAT only 1
- CSF: NAAT only 1
- Venous blood: Serological assays for screening or when lesions absent 1
Why HSV Typing Matters
- Type differentiation is essential - HSV-1 causes up to 50% of first-episode genital herpes but has less frequent recurrences and subclinical shedding compared to HSV-2 2
- Typing affects counseling regarding natural history, recurrence risk, and transmission probability 1, 2
- Use assays that differentiate HSV-1 from HSV-2 to provide accurate prognostic information 1