Diagnostic Testing for Genital Herpes
Nucleic acid amplification testing (NAAT/PCR) from swabs of active genital lesions is the first-line diagnostic test for genital herpes, as it provides superior sensitivity and allows simultaneous HSV-1 and HSV-2 typing in a single reaction. 1, 2
Primary Diagnostic Approach
For Patients with Active Lesions
PCR testing should be performed on samples from vesicular fluid or ulcer bases, as this method demonstrates 11-71% superior sensitivity compared to viral culture and provides results within approximately 2 hours. 1, 2
Optimal sample collection technique varies by lesion type:
- Vesicular lesions: Open vesicles with a sterile needle and collect fluid with a cotton-wool or Dacron swab (yields 90% detection rate with culture, even higher with PCR) 2, 3
- Ulcerative lesions: Swab the base of the ulcer after removing any purulent discharge 1, 2
- Avoid crusted lesions: Detection rates drop dramatically to only 27% even with optimal methods 2
Anatomic site-specific sampling:
- Males with urethral involvement: Clean the external urethral opening with saline-moistened swab, then insert swab 0.5-2 cm into the urethral meatus 2, 3
- Females: Collect from cervical canal (2 cm depth) or vaginal wall using cotton-wool or Dacron swab on aluminum shaft 2, 3
- External genital lesions: Direct swabbing of lesion base after cleaning 1
Alternative Testing When PCR Unavailable
Viral culture serves as the second-choice diagnostic method if NAAT is unavailable, though it has significantly lower sensitivity, particularly for ulcerative (70% detection) or crusting lesions (27% detection). 1, 2 Samples for viral culture must be transported on ice and processed within 24 hours to maintain viral viability. 2, 3
Antigen detection methods (immunofluorescence or enzyme immunoassay) can be employed for symptomatic patients but are less sensitive than PCR. 2, 4
Type-Specific Serologic Testing
Type-specific serology based on glycoprotein G (with approximately 97% sensitivity and 98% specificity) should be used in specific clinical scenarios:
- Patients with genital lesions where PCR, culture, or antigen detection failed to detect HSV 1, 5
- Asymptomatic individuals with history suggestive of genital herpes 1, 5
- HIV-infected persons 5
- Pregnant women at risk of acquiring HSV close to delivery 1
- Evaluation of couples discordant for genital herpes 5
Widespread screening for HSV antibodies in asymptomatic populations is NOT recommended. 1, 4
Critical Testing Pitfalls to Avoid
Never rely solely on clinical diagnosis without laboratory confirmation, as this leads to both false positive and false negative results—clinical differentiation from other causes of genital ulceration (syphilis, chancroid, Behçet syndrome, Crohn disease) is unreliable. 2, 3
Do not use Tzanck smears or cytological examinations as they have poor sensitivity and specificity. 2, 1
Avoid HSV-specific IgM testing to diagnose recent infection, as approximately one-third of patients with recurrent HSV-2 have IgM responses, making it a poor indicator of acute infection. 2
Do not use HSV molecular assays in the absence of genital ulcers for routine screening purposes. 1
Essential Testing Considerations
HSV typing (distinguishing HSV-1 from HSV-2) is essential because up to 50% of first-episode genital herpes cases are caused by HSV-1, and recurrences and subclinical viral shedding are less frequent with genital HSV-1 than HSV-2, which affects counseling and prognosis. 1, 4
Laboratory confirmation is necessary for estimating infectivity during lesion episodes, identifying persons at risk of subclinical transmission, and selecting women at future risk of transmitting infection to neonates. 3