What is the recommended lab test for diagnosing genital herpes?

Recommended Laboratory Tests for Diagnosing Genital Herpes

For patients with active genital lesions, nucleic acid amplification tests (NAATs) such as PCR should be the first-line diagnostic test for HSV detection due to their superior sensitivity and specificity compared to other methods. 1, 2

Diagnostic Algorithm for Genital Herpes

For Patients with Active Lesions:

• First choice: NAAT/PCR - Offers the highest sensitivity (11-71% superior to viral culture) and allows simultaneous detection and typing of HSV-1 and HSV-2 in a single reaction 1, 3
• Second choice: Viral culture - If NAAT is unavailable, viral culture can be used but has lower sensitivity 1
• Not recommended: Direct immunofluorescence assay and Tzanck smear - These lack sensitivity and are not recommended for diagnosis 1

For Patients without Active Lesions:

• Type-specific serological assays - Should be used for:
  • Asymptomatic individuals at risk 1
  • Pregnant women at risk of acquiring HSV infection close to delivery 1
  • Men who have sex with men 1
  • People who are HIV positive 1
  • Persons who present without lesions or with atypical lesions 1

Sampling Recommendations

• Vesicular lesions: Sample fluid from intact vesicles or base of ulcers 1
• Male patients: Urethral swabs for NAAT or antigen detection 1
• Female patients: Cervical/urethral swabs for NAAT or antigen detection 1
• Other sites: Samples can also be collected from conjunctiva, urine, vulva/vagina, or spinal cord fluid as appropriate 1

Important Considerations

• HSV typing is essential - Differentiation between HSV-1 and HSV-2 is important for counseling and prognosis 1, 2

  • Up to 50% of first-episode genital herpes cases are caused by HSV-1 1
  • Recurrences and subclinical viral shedding are less frequent with genital HSV-1 than HSV-2 1

• Limitations of serological testing:

  • Cannot determine the etiology of a presenting genital lesion with certainty 1
  • HSV-1 assays lack sensitivity, which can result in false-negative diagnoses 1
  • HSV-specific IgM is a poor indicator of recent infection 1
  • Widespread screening for HSV antibodies is not recommended 1

• Sample handling:

  • NAAT allows less strict sample transportation conditions compared to viral culture 1
  • For viral culture, samples should be transported to the laboratory on ice and processed within 24 hours 1

Clinical Pitfalls to Avoid

• Do not rely solely on clinical diagnosis without laboratory confirmation 2, 4
• Avoid using HSV molecular assays in the absence of genital ulcers, as intermittent viral shedding reduces sensitivity 1
• Be aware that healing lesions may become negative for HSV DNA, potentially resulting in false-negative results 1
• Non-validated diagnostic tests should be validated against approved gold standard tests 1
• HSV-2 serology has poor sensitivity (13.33%) for primary genital herpes but better sensitivity (73.33%) for recurrent disease 5