False Positive Herpes Test: What You Need to Know
An in-depth guide to false positive herpes test results, including why they happen, who is most at risk, and what steps to take if you suspect your result may be inaccurate.
By Kind Dating · Community perspective and general information.
False Positives Are More Common Than You Think
One of the least discussed aspects of herpes testing is the rate of false positive results, particularly with the standard IgG blood test for HSV-2. A false positive means the test says you have herpes when you actually do not. This is not a rare occurrence, and understanding when and why it happens can save you significant distress.
The issue is most pronounced with HSV-2 IgG results in the low-positive range. CDC notes that the most commonly used HSV-2 test is often falsely positive at index values of 1.1 to 3.0, and one study found a specificity of only 39.8 percent in the 1.1 to 2.9 range. The USPSTF estimates the test's positive predictive value in the US population may be as low as 50 percent, meaning up to half of positive results could be false. The lower the prevalence in the group being tested, the higher the chance that a low-positive result is false.
CDC recommends that low-index results be confirmed with a second test method, such as the Biokit test or a Western blot, before they are interpreted. Even so, not every provider mentions this, and a low-positive result is sometimes delivered as a definitive diagnosis, so it is worth asking.
Why False Positives Happen
The IgG antibody test detects antibodies that your immune system produces against specific herpes proteins: glycoprotein G2 (gG2) for HSV-2 and glycoprotein G1 (gG1) for HSV-1. The reasons for false positives are technical, but the pattern is well documented: results just above the cutoff are much less reliable than strongly positive results.
A different kind of herpes blood test, the IgM test, causes its own confusion. ASHA notes that IgM tests can cross-react with related viruses such as varicella zoster (the chickenpox virus) and cytomegalovirus and cannot reliably tell HSV-1 from HSV-2, and CDC does not recommend them.
The test's positive predictive value (the probability that a positive result is truly positive) depends heavily on the prevalence of HSV-2 in the population being tested. In populations where HSV-2 is less common, the false positive rate is higher. This is a fundamental property of all screening tests and is not unique to herpes testing.
How to Know If Your Result Might Be False
The single most important factor is your index value. If your HSV-2 IgG index value is between 1.1 and 3.0, there is a meaningful chance the result is a false positive, and CDC recommends confirmatory testing. Higher values are more likely to be accurate, but your provider can help you interpret your specific result.
Your clinical history also matters. If you have never had any symptoms suggestive of genital herpes, never had a partner with known HSV-2, and have a low-positive IgG result, the probability of a false positive increases. Conversely, if you have a history of genital symptoms consistent with herpes, even a low-positive result is more likely to be accurate.
Ask your healthcare provider for your exact index value, not just a "positive" or "negative" result. The number matters significantly. If your provider cannot provide the index value, request the full lab report.
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A common step for confirming or refuting a low-positive IgG result is the Western blot test, performed at the University of Washington. The lab says the test distinguishes HSV-1 from HSV-2 antibodies accurately in 99 percent of patients, which makes it a strong tool for resolving ambiguous results. CDC also lists the Biokit test as a confirmatory option.
To access the Western blot, you will need a healthcare provider to order the test. Some providers are familiar with the process, while others may need guidance; the University of Washington publishes ordering information for clinicians. Ask about cost and insurance coverage before ordering.
While waiting for confirmatory results, try to avoid making major life decisions based on a potentially inaccurate test. This is easier said than done, but understanding that false positives are a known and documented issue can help you maintain perspective.
The Emotional Impact of a False Positive
Receiving a positive herpes test result, even one that turns out to be false, can be emotionally devastating. Many people experience grief, shame, anxiety about dating, and changes to their self-image. If the result is later overturned by the Western Blot, the emotional damage has already been done.
This is part of why the US Preventive Services Task Force recommends against routine blood-test screening for people without symptoms. It judged that the harms, including false-positive results and the anxiety and relationship disruption they can cause, outweigh the benefits of screening everyone.
If you are going through the uncertainty of a potential false positive, connecting with the HSV community can be helpful regardless of your final result. Communities like Kind and various online support groups can provide perspective and support during a stressful time.
Advocating for Accurate Testing
If you want a herpes test, be an informed consumer. Ask for a type-specific IgG test and request the index value with your results. If the result is low-positive for HSV-2, ask about confirmatory Western Blot testing before accepting the diagnosis as definitive.
If you have an active lesion, insist on a PCR swab test rather than relying solely on blood testing. PCR from an active lesion is far more definitive than antibody testing and provides clear type identification.
Herpes testing is imperfect, but understanding its limitations allows you to navigate the process with clearer eyes. You deserve accurate information about your health, and advocating for proper testing is an important part of getting it.
Sources
- Genital Herpes: Sexually Transmitted Infections Treatment Guidelines, 2021 — Centers for Disease Control and Prevention
- Genital Herpes Infection: Serologic Screening (2023 recommendation) — U.S. Preventive Services Task Force
- Viral Serology: Herpes Simplex Virus Types 1 and 2 by Western Blot — University of Washington Virology
- Herpes Testing — American Sexual Health Association
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for diagnosis, treatment, and answers to your personal health questions. Statistics cited are from publicly available sources including the WHO and CDC and may be updated as new research becomes available.
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