What laboratory tests are ordered for the diagnosis of oral herpes?

Laboratory Testing for Oral Herpes

For diagnosing oral herpes, nucleic acid amplification tests (NAATs) from vesicular lesions are the preferred diagnostic method due to their superior sensitivity and specificity compared to other testing methods. 1

Optimal Testing Approach for Oral Herpes

Primary Testing Method

• NAAT/PCR from lesion samples:
  • Collect specimen by opening vesicles with a sterile needle and swabbing the base of the lesion 1
  • Offers >90% sensitivity and specificity 1
  • Should differentiate between HSV-1 (most common in oral herpes) and HSV-2 1
  • Allows for less strict sample transportation conditions compared to viral culture 1

Alternative Testing Methods (if NAAT unavailable)

1. Viral Culture:

   • Traditional method but less sensitive than NAAT (90% from vesicular lesions, 70% from ulcerative lesions, only 27% from crusting stage) 1
   • Advantage: allows virus typing and antiviral sensitivity testing 1
   • Disadvantage: requires strict sample transportation conditions and takes 24-72 hours (up to 5 days) for results 1

2. Antigen Detection:

   • Direct immunofluorescence (DIF) or enzyme immunoassay (EIA) 1
   • Less sensitive than NAAT but can be employed if NAAT is unavailable 1
   • DIF has sensitivity of 70-90% compared to culture for symptomatic patients 1

Testing to Avoid

• Tzanck smear: Lacks sensitivity and is not recommended 1
• Non-type-specific serologic tests: Cannot determine if HSV antibodies are from oral or genital infection 1

Specimen Collection Technique

• Open vesicles with a sterile needle
• Collect vesicle content with a swab
• For optimal results, collect from:
  • Fresh vesicles (highest yield)
  • Base of the ulcer if vesicles have ruptured
  • Perioral skin or vermillion part of the lip (HSV is rarely detected from oral mucosa in immunocompetent patients with recurrent infection) 2

When to Consider Serologic Testing

• Type-specific serologic tests (targeting HSV glycoprotein G) should be used when:
  • No active lesions are present but clinical suspicion is high 3
  • Lesions have healed and NAAT/culture results were negative or not performed 1
  • Evaluating asymptomatic individuals at risk 1

Important Clinical Considerations

• Timing matters: Testing yield decreases as lesions heal 1
• HSV-1 causes approximately 80-90% of oral herpes cases, while HSV-2 is uncommon in the oral cavity (found in only 3.2% of patients with HSV-2 infection) 4
• False negatives can occur if:
  • Lesions are already healing
  • Sampling technique is poor
  • Sample transportation conditions are inadequate
  • Testing is performed during the window period (for serologic tests) 1

Common Pitfalls to Avoid

• Testing mucosal sites without visible lesions has poor sensitivity due to intermittent viral shedding 1
• Relying solely on clinical appearance for diagnosis (laboratory confirmation is essential) 1
• Using non-type-specific serologic tests that cannot distinguish between HSV-1 and HSV-2 1
• Interpreting positive HSV-1 serology as evidence of oral herpes (could be from asymptomatic infection) 1

By following this evidence-based approach to laboratory testing, clinicians can accurately diagnose oral herpes infections and provide appropriate treatment and counseling to patients.