What is the recommended initial test for diagnosing genital herpes?

Laboratory Testing for Genital Herpes

Polymerase chain reaction (PCR) testing from a swab of active genital lesions is the recommended initial test for diagnosing genital herpes, as it has 11-71% superior detection rates compared to viral culture and is now considered the gold standard. 1, 2, 3

Optimal Testing Approach

First-Line Test for Active Lesions

• PCR (nucleic acid amplification test) should be performed on swabs from vesicular or ulcerative genital lesions as it provides the highest sensitivity and specificity for HSV detection 1, 2, 3
• PCR allows simultaneous detection and typing (HSV-1 vs HSV-2) in a single reaction tube, with results available in approximately 2 hours 1
• Type-specific testing to distinguish HSV-1 from HSV-2 is always recommended since viral type affects prognosis and counseling 2, 3

Sample Collection Technique

For vesicular lesions:

• Open vesicles with a sterile needle and collect vesicular fluid with a cotton-wool or Dacron swab 1
• Fresh vesicles yield the highest detection rates (90% for viral culture, even higher for PCR) 1

For male patients with urethral involvement:

• Clean the external urethral opening with saline-moistened swab 1
• Insert swab 0.5-2 cm into the urethral meatus to collect exudates 1

For female patients:

• Collect from cervical canal (2 cm depth) or vaginal wall using cotton-wool or Dacron swab on aluminum shaft 1
• Self-collected vaginal swabs are acceptable and show excellent sensitivity 4

Alternative Testing Methods

• Viral culture can be used as an alternative but has significantly lower sensitivity, particularly for ulcerative (70% detection) or crusting lesions (27% detection) 1
• Viral culture requires 24-72 hours (up to 5 days) for results and strict refrigeration during transport 1
• Antigen detection (immunofluorescence or enzyme immunoassay) can be employed for symptomatic patients but is less sensitive than PCR 1, 2

Testing in Specific Clinical Scenarios

Patients Without Active Lesions

• Type-specific serologic testing based on glycoprotein G should be used for asymptomatic individuals or those with atypical presentations 1, 3
• Serologic assays have approximately 97% sensitivity and 98% specificity 1
• However, widespread screening for HSV antibodies in asymptomatic populations is not recommended 1, 5

When Laboratory Confirmation is Essential

Laboratory confirmation should always be sought because clinical diagnosis alone leads to both false positive and false negative results 1

Test the following patients:

• Males with vesicular/ulcerative lesions on penis, buttocks, or perineum 1
• Females with vesicular/ulcerative lesions on genitals, buttocks, or thighs 1
• Patients with dysuria following treatment for gonorrhea or nongonococcal urethritis 1
• Sexual contacts of proven genital herpes cases 1
• Newborns with vesicles or crusts whose mothers had genital herpes during pregnancy 1

Critical Pitfalls to Avoid

Sample Collection Errors

• Do not rely on samples from crusted lesions as detection rates drop to 27% even with viral culture 1
• Avoid touching the swab tip with fingers or allowing contact with other surfaces 4
• Do not use excessive force when inserting swabs 4

Diagnostic Test Limitations

• Never rely on Tzanck smears or cytological examinations as they have low sensitivity and specificity 6
• Do not use 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 1
• Remember that HSV and Treponema pallidum can occasionally be recovered from the same lesion, so consider syphilis testing in appropriate clinical contexts 1

Transportation Requirements

• PCR samples tolerate less strict transportation conditions compared to viral culture 1
• Viral culture samples require refrigeration during transport to maintain viability 1, 6
• Delayed transport and lack of refrigeration substantially affect viral culture outcomes 1

Clinical Context

The difficulty in clinical diagnosis, combined with the growing worldwide prevalence (affecting over 400-500 million people) and availability of effective antiviral therapy, makes rapid and accurate laboratory diagnosis essential 2, 7, 5