What is the role of serological testing in diagnosing Herpes Simplex Virus (HSV) infection?

Serological Testing for HSV Diagnosis

Direct Answer

Serological testing for HSV should be reserved for specific clinical scenarios—primarily when active lesions are absent or have healed, when confirming asymptomatic infection in high-risk populations, or when NAAT/PCR from lesions is negative but clinical suspicion remains high—and should never be used as first-line testing when active genital lesions are present. 1, 2

When to Use Serological Testing

Appropriate Clinical Scenarios

• Use type-specific HSV-2 serology when no active lesions are present and you need to diagnose genital herpes in patients with a history of genital symptoms but no current ulcers, as NAAT/PCR requires active lesions for adequate sensitivity 1, 2

• Order serological testing for high-risk asymptomatic individuals, specifically: pregnant women at risk of acquiring HSV near delivery, men who have sex with men, HIV-positive patients, and sexual partners of persons with known genital herpes 2, 3, 4

• Consider serology when NAAT/PCR or viral culture from lesions is negative but clinical suspicion for HSV-2 remains high, particularly to rule out HSV-2 infection 1

• Do not use serological testing for widespread screening in the general asymptomatic population, as this is not recommended by the CDC or USPSTF 3, 4

When NOT to Use Serological Testing

• Never order serology when active genital lesions are present—this is a critical error that misses the opportunity for definitive NAAT/PCR diagnosis from the lesion itself 1, 2

• Do not use HSV-1 serology to diagnose genital herpes, as it has only 70.2% sensitivity (frequent false-negatives) and cannot distinguish oral from genital infection 1, 2

Understanding Test Performance and Limitations

HSV-2 Serology Characteristics

• Sensitivity is high at 92%, but false-negatives occur during the 12-week window period after initial infection 1, 3

• Specificity is highly dependent on the index value reported: index values of 1.1-2.9 have only 39.8% specificity, while values ≥3.0 have 78.6% specificity 1, 2, 4

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

HSV-1 Serology Characteristics

• HSV-1 antibody detection has poor sensitivity at only 70.2%, resulting in frequent false-negative results that limit clinical utility 1, 2

Algorithmic Approach to Ordering and Interpreting Serology

Step 1: Initial Testing Strategy

• Order type-specific HSV-2 IgG testing using glycoprotein G-based EIA or CLIA as the first-line serological test 2, 4

• Ensure the assay differentiates HSV-1 from HSV-2, as this provides critical prognostic information—HSV-2 causes more frequent recurrences and subclinical shedding than HSV-1 genital infections 1, 4

Step 2: Interpret Results Based on Index Values

• Index value <0.9 = Negative: No HSV-2 antibodies detected, but consider the 12-week window period if recent exposure is suspected 1, 2

• Index value 0.9-1.1 = Indeterminate: Repeat testing in 2-4 weeks or confirm with alternative assay 1, 2

• Index value 1.1-2.9 = Low positive requiring confirmation: This range has only 39.8% specificity and high false-positive rates, especially in HSV-1 positive patients 1, 2

• Index value ≥3.0 = Positive: This range has 78.6% specificity and is more reliable 1, 2

Step 3: Confirmatory Testing for Low-Positive Results

• For index values 1.1-2.9, confirm with a second assay using a different glycoprotein G antigen, which improves specificity from 93.2% to 98.7% and positive predictive value from 80.5% to 95.6% 2

• The Western blot/immunoblot is the gold standard for confirmation but is not widely available in clinical practice 1, 2

Step 4: Timing Considerations

• Wait at least 12 weeks after potential exposure before ordering serology to avoid false-negatives during the window period 1, 3

• Do not repeat negative serology until 12 weeks after exposure to determine if HSV-2 was acquired 1

Critical Pitfalls to Avoid

Common Diagnostic Errors

• Reporting low-positive results (index 1.1-2.9) without confirmation leads to false-positive diagnoses with devastating psychological and relationship consequences 2

• Testing too early after exposure will miss infections due to the 12-week antibody development window 2, 3

• Ordering serology when active lesions are present wastes the opportunity for definitive NAAT/PCR diagnosis, which has >90% sensitivity and specificity 1, 3

• Using only a single serological test in patients with recurrent genital herpes can yield false-negatives in 12-30% of cases—commercial type-specific gG assays miss antibodies in a substantial proportion of patients with proven recurrent HSV infection 5

Clinical Context Matters

• Serology cannot diagnose acute genital lesions, as positive results may reflect chronic infection rather than the current episode, and negative results may miss recent infection 6

• HSV-1 serology is unreliable for genital herpes diagnosis due to poor sensitivity and inability to determine anatomic site of infection 1, 2

Counseling Patients with Positive Serology

• A positive HSV-2 IgG indicates past exposure and ongoing latent infection with antibodies persisting indefinitely 3

• Counsel patients that HSV-2 is not curable, that asymptomatic viral shedding occurs, and that transmission can happen even without visible lesions 3, 7

• Recommend safer sex practices in combination with suppressive antiviral therapy to reduce transmission risk 7

• Inform sex partners that they might be infected even if asymptomatic, and that type-specific serologic testing can determine their risk for HSV-2 acquisition 7