How Accurate Are Herpes Blood Tests? What the Numbers Really Mean

If you’ve recently taken a herpes blood test, you may be wondering how accurate your result really is. While blood tests are a helpful tool for detecting HSV-1 and HSV-2, they’re not perfect. The reliability of your test depends on factors like timing, type of test used, and your specific result values.

This page breaks down how herpes blood tests work, what affects their accuracy, and what to do if you’re uncertain about your results. Whether you’re trying to confirm an exposure or just want peace of mind, knowing how to interpret your results is key.

How Do Herpes Blood Tests Work?

Most herpes tests are **type-specific IgG antibody tests**, which detect antibodies to either HSV-1 or HSV-2 in your blood. These antibodies are produced by your immune system in response to infection. Once they appear, they usually remain for life—so a positive result generally means you’ve been exposed at some point, even if you’ve never had symptoms.

Both STDCheck and myLAB Box use FDA-cleared IgG tests, which are considered reliable when used at the right time and interpreted correctly.

How Accurate Are These Tests?

Accuracy varies depending on several factors:

• HSV-2: Type-specific IgG tests for HSV-2 are generally considered **highly accurate** when performed at least 12 weeks after exposure. Specificity is around 95–98%.
• HSV-1: Testing for HSV-1 is more complicated. Antibodies are more common due to childhood exposure, and the test can sometimes pick up weak signals or cross-reactivity. This leads to **more false positives** than HSV-2 testing.

Timing is critical. Testing too soon—before your body has had time to build antibodies—can result in a **false negative**. That’s why most labs recommend waiting 4 to 6 weeks after exposure, and ideally retesting at 12 weeks if the first test is negative.

What Do Index Values Mean?

Herpes blood test results often come with an “index value,” which reflects how strongly the test detected antibodies:

• Below 0.9: Negative
• 0.9–1.1: Equivocal (uncertain)
• 1.1–3.5: Low positive – may require confirmation
• Above 3.5: Strong positive – typically accurate

If your value falls between 1.1 and 3.5, it’s a good idea to confirm the result with a second test. Research suggests up to 50% of low-positive HSV-2 results may be false. For more on this, visit our false positives guide.

What If Your Test Is Negative?

A negative result is usually reassuring, especially if it comes 12 or more weeks after your last possible exposure. However, false negatives can still happen—particularly if you tested too early or your immune response is slow to develop.

If you tested early and have ongoing concerns, you can retest using either an at-home kit or a lab-based provider like STDCheck. Testing again a few weeks later can provide a more accurate picture of your status.

Factors That Can Affect Accuracy

• Timing: Antibodies may take weeks to appear, especially for HSV-2.
• Cross-Reactivity: Other viruses like EBV or CMV can sometimes interfere.
• Test Quality: FDA-cleared tests are better than older or non-type-specific methods.
• Your Immune Response: Individual variation plays a role.

Understanding these factors can help you put your test results in context. No single result should be taken as final without considering when it was taken, how it was performed, and whether you’ve had any symptoms or known exposures.

What to Do If You’re Still Unsure

If you received a low positive or an equivocal result, it’s reasonable to retest. STDCheck allows you to order HSV-1 and HSV-2 tests separately, while myLAB Box offers at-home HSV-2 screening with a free telehealth consult included if your result is positive.

Getting tested again—whether now or in a few weeks—can help clear up doubts and allow you to move forward with confidence.

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