Herpes Simplex Virus type 2 (HSV-2) is a common sexually transmitted infection often screened using blood tests. Standard antibody test results are usually reported as positive or negative. An “equivocal” result, however, causes confusion because it offers no clear answer about infection status. This technical term indicates statistical uncertainty in the laboratory assay. This article clarifies what an HSV-2 equivocal test result means and outlines the steps needed to gain a definitive diagnosis.
Understanding Equivocal Test Results
The standard screening method for past HSV-2 exposure is a type-specific blood test that detects Immunoglobulin G (IgG) antibodies. The body produces these antibodies in response to the virus, and they remain detectable for life. The test measures the concentration of these antibodies, converting it into a numerical Index Value.
An equivocal result means the Index Value falls into a narrow statistical “gray zone” between the established cutoff thresholds for positive and negative results. For example, a result below 0.9 is negative, while a result at or above 1.1 is positive. The equivocal range typically exists within this narrow window, such as between 0.91 and 1.09.
This ambiguity signals that the antibody concentration is too low for a positive result, but too high to be dismissed as negative. The inconclusive result requires further investigation and reflects the test’s limitations.
Primary Reasons for Equivocal Readings
Equivocal readings occur due to biological or technical reasons related to the timing or nature of the immune response.
Recent Infection (Seroconversion)
One common reason is a very recent infection where the body is undergoing seroconversion. During this period, which can take several weeks or months after exposure, antibody levels are rising but have not yet stabilized above the positive cutoff.
Cross-Reactivity
Another factor is potential cross-reactivity with the related Herpes Simplex Virus type 1 (HSV-1). Because the two viruses share structural similarities, the immune system may produce a weak, non-specific antibody response that mistakenly reacts to the HSV-2 test. This signal can push the Index Value into the equivocal range, especially in individuals who already carry HSV-1.
Other Factors
Individuals who naturally produce lower levels of antibodies, even if infected, may perpetually test in the equivocal or low-positive range. Technical limitations of the assay itself can also be a factor, as low index values are statistically associated with a higher likelihood of being false positives.
Immediate Next Steps After Equivocal Results
The most immediate step after receiving an equivocal HSV-2 result is consulting a healthcare provider or sexual health clinic. They will evaluate the result within the context of the person’s clinical history, including recent symptoms or known exposures. The initial equivocal result should be treated as an indeterminate finding, not a positive diagnosis.
The standard recommendation is a waiting period followed by a repeat IgG antibody test. Antibody levels generally stabilize around 12 weeks after potential exposure. Retesting is often scheduled 4 to 12 weeks after the initial blood draw to allow the body sufficient time to fully develop a strong antibody response.
During this period of diagnostic uncertainty, adopting safe practices prevents potential transmission. Since the infection status is unknown, using barrier methods like condoms or practicing abstinence is recommended until a definitive diagnosis is established.
Follow-Up Testing Methods and Interpretation
If the repeat IgG antibody test remains equivocal, or if the initial result is unexpected given the person’s risk profile, more definitive testing methods are available.
Western Blot
The Herpes Western Blot is considered the gold standard for confirming HSV-2 serologic results. This test is highly accurate, but it is typically more expensive and only available through specialized reference laboratories.
PCR Testing
Polymerase Chain Reaction (PCR) testing is another option, but it is only useful if the person is currently experiencing symptoms like lesions or sores. The PCR test detects the viral DNA directly from a swab of the lesion, confirming the presence of the active virus. However, it cannot diagnose an asymptomatic infection and is not a relevant follow-up for an asymptomatic equivocal blood test.
The follow-up process leads to one of three possible outcomes. A rising Index Value or a positive Western Blot confirms a definitive positive diagnosis. Conversely, a falling Index Value or a negative Western Blot establishes a definitive negative status. Rarely, a result remains indeterminate even after follow-up testing, which usually prompts the provider to treat the result as negative for primary or recent infection, especially if the person has a low risk of exposure.