The Accuracy of a Herpes Blood Test

While not be perfect, the good ones are very good

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Wondering if you've contracted herpes simplex virus (HSV) can be incredibly stressful. Whether you're experiencing symptoms or have reason to believe you've been exposed, it's important for you to get tested and confirm a diagnosis.

The most accurate way of determining whether or not you have herpes is to get a blood test designed to detect the virus.

A blood sample being held with a row of human samples for analytical testing including blood, urine, chemistry, proteins, anticoagulants and HIV in lab
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Due to the stigma associated with herpes, it is not uncommon for people to worry about getting tested - but getting tested is extremely important for your sexual health and the sexual health of your current or future sexual partners. It's also important to understand how you should interpret your results.

How Accurate Is a Herpes Blood Test?

No test is error-proof, and herpes detection testing is no different. The estimated sensitivity/specificity levels of two different, relatively standard, herpes blood tests are as follows:

ELISA (HSV-1 or HSV-2):

  • Sensitivity: 96%–100%
  • Specificity: 97%–100%

Immunoblot (HSV-1 and HSV-2):

  • Sensitivity: 87%–100%
  • Specificity: 98%

What the Values Mean

What does that mean for you? How common herpes comes into the calculation. It affects how likely positive tests and negative tests are to be correct. In fact, it can make a bigger difference than herpes blood test accuracy!

Let us make the reasonable assumption that around 50% of the population are infected with HSV1. That's the virus primarily associated with oral herpes and cold sores. It's also associated with a growing number of genital herpes infections.

Then assume that 25% of people are infected with HSV2. That's the virus primarily associated with genital herpes. In that scenario, the positive predictive value and negative predictive value are as follows.

ELISA:

  • HSV-1: At least 94% of positive tests give the correct result, and at least 99% of negative test will be correct.
  • HSV-2: At least 98% of positive tests are correct, and at least 97% of negative tests are correct.

Immunoblot:

  • HSV-1: 95% of positive tests are correct, and 97% of negative tests are correct.
  • HSV-2: 99% of positive tests are correct, and 99% of negative tests are correct.

The Problem of False-Positive Tests

Herpes blood tests are actually pretty accurate. That's particularly true for the type-specific tests that are most often recommended.

In a relatively high prevalence population, they give accurate results the vast majority of the time. It's worth noting, though, that if the prevalence estimates are off, it would make a big difference.

What if we worked from the assumption that only 10% of the population was infected with either virus? Then, although almost all negative tests would still be accurate, positive tests would only be correct 55% to 85% of the time. In other words, there would be a lot of false-positive tests.

The possibility of false-positive tests in populations where herpes isn't common is a big concern. In fact, it is one of the reasons that screening for herpes is not widely recommended. Doctors are concerned that the stress of a false positive test may outweigh the benefits of early detection of the virus in someone who is asymptomatic.

The Centers for Disease Control and Prevention estimates that the prevalence of herpes is pretty high. They estimate that by the age of 50, almost 47.8% of adults are infected with HSV1 and 11.9% with HSV2. There are big differences in prevalence that depend on race and sex. 

Still, since herpes can be transmitted in the absence of symptoms and suppressive therapy can help prevent transmission, I don't necessarily agree. I personally believe that people who know they may be at risk can make an informed decision to undergo a herpes blood test to be screened for the virus. That is particularly true if they are in a situation where they could be exposing new sexual partners to the virus.

It is, however, important to understand that false-positive tests can happen. It's also critical to know that, even if you are infected with a herpes virus, living with herpes is not the end of the world.

Frequently Asked Questions

  • What tests are used to diagnose herpes simplex?

    There are two categories of blood tests used to diagnose herpes simplex 1 (HSV-1) and herpes simplex 2 (HSV-2) infection:

    • HSV ELISA (enzyme-linked immunoassays) detects HSV-specific antibodies.
    • HSV Western blot (immunoblot), primarily used to confirm a diagnosis, also detects HSV antibodies.
  • How accurate are herpes blood tests?

    Overall, the accuracy of the newer-generation HSV-1 and HSV-1 blood tests is exceptionally high. The sensitivity (ability to identify people who have a disease) and specificity (ability to identify people who don't have it) vary by the type of test used:

    • HSV-1 ELISA: 94% to 100% sensitivity and 99% to 100% specificity
    • HSV-2 ELISA: 98% to 100% sensitivity and 97% to 100% specificity
    • HSV-1 Western blot: 95% sensitivity and 97% specificity
    • HSV-2 Western blot: 99% sensitivity and 99% specificity
  • Can a herpes test return a false-positive or false-negative results?

    The likelihood of a false-positive result is extremely low but can occur due to user error or improper storage or handling. By contrast, a false-negative result is likely if your body has not produced enough antibodies to reach detectable levels. For this reason, people are advised to wait 12 to 16 weeks from the time of the suspected exposure before getting a test.

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9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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