What to do when a patient is clinically diagnosed with Herpes Simplex Virus type 2 (HSV2) but laboratory tests come back negative?

False Negative HSV2 Test Results in Clinically Diagnosed Patients

When a patient is clinically diagnosed with HSV2 but laboratory tests come back negative, this is most likely due to the limitations of serologic testing, timing of the test, or sampling issues. 1

Reasons for False Negative HSV2 Test Results

Testing Method Limitations

• PCR testing from active lesions is the gold standard with >90% sensitivity and specificity, but can still miss infections 1
• Serologic tests have significant limitations:
  • HSV-1 serologic tests have limited sensitivity (~70%) 2, 1
  • HSV-2 serologic tests have high sensitivity (92%) but variable specificity 2
  • False-negative results occur in up to 12-30% of patients with recurrent HSV-1 or HSV-2 DNA positive genital lesions 3

Timing Issues

• Window period: Serologic testing should not be repeated until at least 12 weeks after exposure to determine if HSV-2 was acquired 2, 1
• Testing during the healing phase of lesions can yield false negatives 1

Sampling Issues

• Inadequate sample collection from lesions
• Improper specimen handling or storage
• Testing inappropriate sites that don't have active viral shedding 2, 1

Recommended Approach for Discordant Results

Step 1: Evaluate the Clinical Presentation

• Assess if the clinical presentation is truly consistent with HSV2 (clustered vesicles, painful ulcers, recurrent nature)
• Consider alternative diagnoses that can mimic genital herpes

Step 2: Determine the Type of Test Used

• If serologic testing was used, consider the limitations mentioned above
• If PCR or viral culture was used, evaluate sampling technique and timing

Step 3: Recommended Testing Algorithm

1. For patients with active lesions:

   • Perform NAAT/PCR testing from the lesion (gold standard) 2, 1, 4
   • If PCR is unavailable, viral culture is an acceptable alternative 2
   • Antigen detection methods (DIF or EIA) can be used if PCR and culture are unavailable 2

2. For patients without active lesions:

   • Type-specific serologic testing using glycoprotein G assays 2, 1
   • If initial test is negative but clinical suspicion is high:
     • Repeat serologic testing after 12 weeks from suspected exposure 2
     • Consider using a different serologic assay 1

3. For patients with low positive HSV-2 serologic results (index value <3.0):

   • Confirm with a second test using a different gG antigen 2, 1
   • Biokit HSV-2 rapid assay or Western blot can be used as confirmatory tests 2

Important Caveats

• Even with index values ≥3.0, false positives have been reported 2, 1
• Persons with HSV-1 infection are more likely to have false-positive HSV-2 test results with low index values 2
• Commercial type-specific HSV antibody assays can be false negative in 12-30% of patients with recurrent HSV DNA positive genital lesions 3
• Using multiple testing methods increases diagnostic accuracy - in one study, 88-90% of patients with recurrent HSV had antibodies detected when using at least one of three different antibody tests 3

Quality Control Considerations

• Ensure proper internal positive controls and negative controls are used in laboratory testing 2
• Consider referral to specialized laboratories for Western blot testing in cases where diagnosis remains uncertain despite repeated testing 2, 1