What is the preferred serological test for diagnosing Herpes Simplex Virus (HSV)?

Optimal Serological Test for Herpes Simplex Virus

The Western blot/immunoblot assay is the gold standard for HSV serological testing, but given its limited availability, type-specific glycoprotein G-based enzyme immunoassays (EIA) or chemiluminescent immunoassays (CLIA) are the practical first-line serological tests, with critical attention to index values and confirmatory testing for low-positive results. 1

Understanding the Gold Standard vs. Practical Reality

The Western blot/immunoblot represents the reference standard because it targets antibodies to multiple HSV antigens beyond glycoprotein G, providing superior accuracy. 1 However, this test has severely limited availability in most clinical settings, making it impractical for routine use. 1

For routine clinical practice, FDA-approved type-specific serological assays that detect antibodies to HSV glycoprotein G-1 or G-2 using EIA or CLIA are the recommended tests. 1, 2 These assays differentiate between HSV-1 and HSV-2, which is essential for counseling and prognosis. 2, 3

Critical Limitations You Must Know

HSV-1 Serology Has Poor Sensitivity

• HSV-1 antibody detection has only 70.2% sensitivity, resulting in frequent false-negative results. 1
• HSV-1 IgG detection is not useful for diagnosing genital ulcer disease and should not be relied upon. 4

HSV-2 Serology Has Specificity Problems

The CDC guidelines emphasize that HSV-2 serologic tests have serious specificity limitations that vary dramatically based on index values: 1

• Index values 1.1-2.9: Only 39.8% specificity (essentially a coin flip)
• Index values ≥3.0: Improved to 78.6% specificity (still imperfect)
• Overall specificity compared to Western blot: only 57.4% 1

Patients with HSV-1 infection are significantly more likely to have false-positive HSV-2 results, especially at low index values. 1

Algorithmic Approach to HSV-2 Serological Testing

Step 1: Initial Testing Strategy

Order a type-specific HSV-2 IgG test using glycoprotein G-based EIA or CLIA (such as HerpeSelect). 1, 2

Step 2: Interpret Based on Index Value

If index value <0.9: Negative result 1

If index value 0.9-1.1: Indeterminate—repeat testing in 12 weeks if recent exposure suspected 1, 2

If index value 1.1-2.9 (low positive):

• Do NOT report as positive without confirmation 1
• Confirm with a second assay using a different glycoprotein G antigen (Biokit HSV-2 rapid assay preferred) 1
• This strategy improves specificity from 93.2% to 98.7% and positive predictive value from 80.5% to 95.6% 1
• If Biokit unavailable, consider Western blot confirmation 1

If index value ≥3.0:

• May be sufficient for diagnosis without confirmatory testing 1
• However, false positives have been documented even at index values >3.5 1
• Consider confirmation in low-prevalence populations 1

Step 3: Timing Considerations

• The window period for HSV-2 antibody development is up to 12 weeks 1, 2
• Do not repeat serological testing until 12 weeks after potential exposure 1
• Sensitivity of HSV-2 serology is 92%, but false negatives occur during the window period 1

When Serology Is NOT the Right Test

Never use serological testing for active genital lesions. 1, 3 In patients with active lesions or ulcers:

• NAAT/PCR from the lesion is first-line, with >90% sensitivity and specificity 1, 2, 3
• NAAT/PCR is 11-71% more sensitive than viral culture 2, 3
• Serology cannot determine the etiology of a presenting genital lesion with certainty 3, 5

Appropriate Clinical Scenarios for Serological Testing

According to the American College of Obstetricians and Gynecologists and CDC, type-specific HSV-2 serology should be used for: 2, 3, 5

• Pregnant women at risk of acquiring HSV infection close to delivery
• Men who have sex with men
• People who are HIV positive
• Detecting asymptomatic infections in high-risk individuals
• Establishing diagnosis when no active lesion is present 6, 7

Widespread screening for HSV antibodies in asymptomatic general populations is NOT recommended. 2, 3, 5

Common Pitfalls to Avoid

1. Reporting low-positive results (index <3.0) without confirmation leads to false-positive diagnoses with significant psychological and relationship consequences 1

2. Testing too early after exposure will miss infections due to the 12-week window period 1, 2

3. Using HSV-1 serology to diagnose genital herpes is unreliable due to poor sensitivity and inability to distinguish oral from genital infection 1, 4

4. Ordering serology when active lesions are present misses the opportunity for definitive NAAT/PCR diagnosis 1, 3

5. Assuming all positive results are accurate without considering the patient's HSV-1 status and the test's index value 1