Which labs can perform a viral culture or PCR test for oral herpes?

Laboratory Testing for Oral Herpes

Nucleic acid amplification tests (NAATs), particularly PCR, are the preferred diagnostic method for oral herpes due to their superior sensitivity and specificity compared to other testing methods. 1, 2

Recommended Laboratory Tests for Oral Herpes

Primary Testing Methods

• Polymerase Chain Reaction (PCR): The gold standard test with highest sensitivity (11-71% superior to viral culture) and specificity for detecting HSV in oral lesions 3, 2
• Viral Culture: Traditional method that can isolate HSV from vesicular or pustular lesions with 90% success rate (though lower for ulcerative or crusting lesions) 3

Secondary Testing Methods

• Antigen Detection Tests:
  • Direct Immunofluorescence (DIF): Allows rapid diagnosis and type differentiation but has suboptimal sensitivity compared to NAATs 3
  • Enzyme Immunoassay (EIA): Sensitivity ≥95% compared to viral isolation, but most commercially available assays don't differentiate between HSV types 3

Sample Collection and Handling

• Optimal Sample: Swab from vesicular rash or mucous membranes of the oral cavity 3
• Collection Timing: Best results when collected from fresh vesicles (90% isolation rate) rather than ulcerative (70%) or crusting lesions (27%) 3
• Transportation:
  • For viral culture: Samples should be refrigerated during transport to maintain viability 3
  • For PCR: Less strict transportation conditions are acceptable 3

Laboratory Capabilities and Considerations

Viral Culture

• Facilities: Requires specialized cell culture capabilities using cell lines such as MRC-5, Vero cells, baby hamster kidney, or rabbit kidney cells 3
• Processing Time: Results typically available in 24-72 hours but may take up to 5 days 3
• Advantages: Demonstrates active infection and allows virus typing and antiviral sensitivity testing 3

PCR Testing

• Processing Time: Approximately 2 hours, significantly faster than viral culture 3
• Advantages: Higher detection rates, allows detection and typing in a single reaction tube 3

Test Selection Algorithm

1. For active lesions:

   • First choice: PCR test (highest sensitivity and specificity) 1, 2
   • Alternative: Viral culture (if PCR unavailable) 3

2. For recurrent episodes or suspected asymptomatic shedding:

   • PCR is strongly recommended due to higher sensitivity 2

3. When no active lesions are present:

   • Type-specific serological tests based on glycoprotein G can detect past infection but cannot determine the site of infection 1

Important Caveats

• Cytological examinations like Tzanck smears have low sensitivity and specificity and should not be relied upon 3
• Commercial type-specific antibody assays may yield false-negative results in 12-30% of patients with recurrent HSV infections 4
• Oral HSV-2 is uncommon compared to oral HSV-1, occurring primarily during first episodes of genital HSV-2 or during genital recurrences 5
• Quality control is essential: laboratories should use internal positive controls and negative controls with each DNA extraction and analysis 3