What is the best initial test for a suspected case of herpes?

Nucleic Acid Amplification Testing (NAAT)/PCR is the Best Test for Suspected Herpes

For suspected cases of herpes, nucleic acid amplification testing (NAAT)/PCR should be the first-line diagnostic test due to its superior sensitivity and specificity compared to all other available methods. 1

Diagnostic Algorithm for Suspected Herpes

1. When Lesions are Present:

• Primary Test: NAAT/PCR from lesion sample

  • Most FDA-approved tests have >90% sensitivity and specificity 2
  • Can detect and differentiate between HSV-1 and HSV-2 in a single test 1
  • Results available within approximately 2 hours 2
  • Requires less strict sample transportation conditions 2

• Sample Collection Technique:

  • Open vesicles with a sterile needle
  • Collect content with a swab
  • Place in appropriate transport media for NAAT 2
  • Collect samples as early as possible in lesion development 1

• Alternative if NAAT Unavailable: Viral culture

  • Less sensitive than NAAT (70% for ulcerative lesions, 27% for crusting lesions) 2
  • Results take 24-72 hours, sometimes up to 5 days 2
  • Significantly affected by transportation conditions 2

2. When No Lesions are Present:

• Type-specific serologic testing is the appropriate choice 2, 1
  • Note: Serologic tests have limitations:
    • HSV-1 assays lack sensitivity (around 70%)
    • HSV-2 serologic tests lack specificity (as low as 57%) 1

Important Considerations

Sample Collection Based on Anatomical Site:

• Genital Lesions: Directly swab vesicle or ulcer
• Male Urethra: Insert swab 0.5-2 cm into urethral meatus 2
• Female Genital Tract:
  • Cervix: Insert swab 2 cm into cervical canal
  • Vagina: Collect material from back wall of vagina 2

Common Pitfalls to Avoid:

1. Relying solely on clinical diagnosis - Laboratory confirmation is essential as clinical features can be misleading 2
2. Using NAAT in the absence of visible lesions - Not sensitive due to intermittent viral shedding 1
3. Delayed transport of samples - Significantly reduces sensitivity, especially for viral culture 2
4. Using non-type-specific tests - Always use assays that differentiate between HSV-1 and HSV-2 2, 1
5. Using outdated methods - Direct immunofluorescence assay and Tzanck smear lack sensitivity and are not recommended 2

Special Situations:

• Healing lesions: May yield false-negative results; consider serologic testing if clinical suspicion is high 2
• Immunocompromised patients: More likely to have atypical presentations; laboratory confirmation is crucial 3
• Pregnancy: Accurate typing is essential for management; consider both NAAT and type-specific serology 4

By following this evidence-based approach to herpes testing, clinicians can ensure accurate diagnosis, appropriate treatment, and effective counseling regarding prognosis and transmission risk.