Testing for HSV-1 and HSV-2 depends on whether you currently have symptoms. If you have an active sore or blister, the most accurate option is a PCR swab taken directly from the lesion. If you have no visible symptoms but want to know your status, a type-specific IgG blood test can detect antibodies to each virus separately. These two approaches work differently, have different accuracy levels, and are suited to different situations.
Swab Tests: Best During an Active Outbreak
When you have a visible sore, bump, or blister, a swab test gives the most reliable answer. A clinician collects fluid from the lesion using a swab, and the sample is sent to a lab for analysis. There are two types of swab tests, and they are not equally useful.
PCR (polymerase chain reaction) is the preferred method. It amplifies tiny amounts of viral DNA from the sample, making it extremely sensitive. In comparative studies, PCR detected the virus in roughly 86% of confirmed cases, while traditional viral culture caught only about 43%. When specimens that were positive by only one method were analyzed separately, PCR reached 100% sensitivity compared to 50% for culture. Both methods have 100% specificity, meaning a positive result from either test is trustworthy. PCR also reliably distinguishes HSV-1 from HSV-2.
Viral culture, the older method, involves growing the virus from the swab sample over 5 to 14 days. It’s less sensitive, requires careful specimen handling, and doesn’t always differentiate between the two types. Most labs have shifted to PCR, but some still offer culture. If you’re getting a swab test, it’s worth confirming that PCR is being used.
Timing matters for swab tests. They work best on fresh lesions that haven’t started to crust over. Once a sore begins healing, the amount of virus on the surface drops, and the test is more likely to miss it. If you develop a suspicious sore, getting swabbed within the first 48 hours gives the best chance of an accurate result.
Blood Tests: Detecting Past Infection
Blood tests don’t look for the virus itself. They detect antibodies your immune system produces in response to infection. The key test is a type-specific IgG antibody test, which uses a protein called glycoprotein G to distinguish HSV-1 (gG-1) from HSV-2 (gG-2). This is the only blood test approach that can tell the two types apart.
The most widely used commercial version of this test has sensitivity ranging from 69% to 100% and specificity between 93% and 100%, depending on the population tested. That’s generally good, but the accuracy gap creates a specific problem with borderline results, which is covered below.
IgG antibodies don’t appear immediately after infection. They develop gradually and aren’t reliably detectable until at least two weeks post-exposure, though many experts recommend waiting 6 to 12 weeks for the most dependable result. Testing too early can produce a false negative simply because your body hasn’t made enough antibodies yet.
Why IgM Tests Are Unreliable
You may see IgM antibody tests offered, sometimes as part of a standard STI panel. Avoid them. IgM testing for herpes is not recommended for clinical use because it cross-reacts with other herpes viruses (like the ones that cause chickenpox or mono), producing results that are essentially meaningless. A positive IgM result doesn’t confirm a new herpes infection, and a negative one doesn’t rule it out. If a provider orders an IgM test, ask for a type-specific IgG test instead.
Understanding Your IgG Results
IgG blood test results come back as an index value, not just positive or negative. The standard cutoffs work like this:
- Below 0.90: Negative
- 0.90 to 1.09: Equivocal (borderline, should be retested)
- 1.10 and above: Positive
Here’s the catch: not all positives are equal. CDC guidelines flag initial HSV-2 IgG results with index values between 1.1 and 3.0 as needing confirmation with a second test method. In this “low positive” range, the risk of a false positive is significantly higher. A value of 1.2, for example, is much less reliable than a value of 8.0. If your result falls in this zone, a confirmatory test is the logical next step before drawing any conclusions.
Confirmatory Testing With Western Blot
The gold standard for confirming HSV antibody status is the Western blot, a lab technique that separates viral proteins and tests your blood against them individually. It’s far more precise than standard IgG screening tests and can definitively distinguish HSV-1 from HSV-2.
The most established version of this test is offered through the University of Washington’s Clinical Virology Lab. It requires a blood draw (5 mL in a serum separator tube), and samples from outside labs must be frozen and shipped on dry ice within specific timeframes. This test is not FDA-cleared but has well-established performance characteristics developed at UW. It’s not a first-line test. You’d use it to confirm or rule out a low-positive IgG result, or to resolve conflicting results from other tests.
At-Home Testing Kits
Several companies now sell at-home herpes testing kits. These typically involve a finger-prick blood sample collected at home and mailed to a lab. Some kits require pricking multiple fingers to get enough blood. The lab runs a type-specific IgG test on the sample and reports results online, usually within a few days.
At-home kits can be convenient if you want privacy or don’t have easy access to a clinic. The underlying lab test is the same IgG methodology used in clinical settings, so the accuracy is comparable. The same limitations apply: a low-positive HSV-2 result (index 1.1 to 3.0) still needs confirmation, and testing too soon after a possible exposure can produce a false negative. At-home kits cannot perform swab testing on active lesions, so they’re only useful for antibody screening.
Why Routine Screening Isn’t Recommended
If you’ve tried to get tested for herpes without symptoms, you may have been told no. That’s not a mistake. Both the CDC and the U.S. Preventive Services Task Force recommend against routine blood screening for genital herpes in people without symptoms, including pregnant individuals. The USPSTF gives this a Grade D recommendation, meaning the potential harms outweigh the benefits.
The reasoning comes down to the false positive problem. In people with no symptoms and no known exposure, the chance that a positive IgG result is actually wrong increases substantially. A false positive herpes diagnosis causes real psychological harm, relationship disruption, and unnecessary treatment, with no clinical benefit. The tests are most useful when there’s a specific reason to use them: a current or recent outbreak, a known exposure, or a partner with a confirmed diagnosis.
Choosing the Right Test for Your Situation
If you have a visible sore right now, get a PCR swab. This gives the most accurate, type-specific result and works regardless of whether you’ve had herpes before. Don’t wait for it to heal.
If you have no symptoms but want to know your status after a specific exposure, a type-specific IgG blood test is the right choice. Wait at least two weeks, and ideally closer to 12 weeks, after the possible exposure. Request HSV-1 and HSV-2 IgG testing specifically, and make sure IgM is not included.
If your IgG result comes back in the low-positive range for HSV-2 (index value 1.1 to 3.0), treat it as unconfirmed and pursue a Western blot or other confirmatory test before accepting the diagnosis. A high-positive result (above 3.5) on a type-specific IgG test is generally reliable without further confirmation.