Testing for HSV-2 depends on whether you have an active sore or not. If a sore or blister is present, a swab test taken directly from the lesion is the most accurate option. If you have no symptoms but want to know your status, a type-specific blood test can detect antibodies, though it comes with important accuracy caveats you should understand before ordering one.
Swab Testing for Active Sores
If you have a visible sore, blister, or ulcer, a swab test is the best way to get a definitive answer. A clinician will take a sample directly from the lesion using a cotton or synthetic swab, then send it to a lab for analysis. Two main methods are used: viral culture and PCR (polymerase chain reaction).
PCR testing is now the preferred method because it’s significantly more sensitive. In comparative studies, PCR swabs detected herpes in 95 to 98% of true positive cases, while traditional viral culture caught about 88%. Both methods are highly specific, meaning false positives from swab tests are extremely rare. PCR also identifies whether the infection is HSV-1 or HSV-2, which matters for understanding your long-term outlook and transmission risk.
Timing matters with swab tests. They work best on fresh, fluid-filled blisters or newly opened sores. Once a lesion has started crusting over or healing, the amount of virus on the surface drops and the test is more likely to come back negative even if herpes caused the sore. If you notice a suspicious lesion, get it swabbed as soon as possible.
Blood Tests When There Are No Symptoms
Blood tests don’t detect the virus itself. They detect antibodies your immune system produces in response to HSV-2 infection. The standard approach uses a type-specific IgG test that targets a protein called glycoprotein G, which differs between HSV-1 and HSV-2. This distinction allows the test to tell you which type you carry, or whether you carry both.
The most widely used screening test is the HerpeSelect IgG ELISA. It produces a numerical index value rather than a simple positive or negative. A result below 0.90 is negative. Values between 0.90 and 1.09 are equivocal, meaning the test can’t make a determination. A value of 1.10 or above is considered positive.
However, and this is the critical part, not all positive results are truly positive.
The False Positive Problem
Low-positive index values, defined as 1.10 to 3.50, have a meaningful false positive rate. Research published in the Journal of Clinical Microbiology found that roughly 21% of HSV-2 results in this low-positive range were false positives when checked against more accurate confirmatory testing. For some assays, the rate was even higher.
This is why the CDC recommends a two-step process: screen first with the standard IgG test, then confirm any low-positive result with a second, more specific test. The gold standard for confirmation is the Western blot, which detects antibody responses to multiple viral proteins rather than just one. A result with an index value above 3.50 is much more likely to be a true positive, though confirmation is still available if you want certainty.
The false positive issue is also the main reason the CDC does not recommend routine herpes blood testing for people without symptoms. The agency specifically notes that herpes blood tests are less precise than tests for STIs like chlamydia or gonorrhea, and that the chances of a wrong result are higher for people at low risk of infection. This doesn’t mean the test is useless. It means you need to interpret results carefully, especially in the low-positive range.
When to Test and the Antibody Window
Your body doesn’t produce detectable antibodies immediately after infection. If you were recently exposed, testing too early can produce a false negative. Research tracking seroconversion found that 50% of people with a new HSV-2 infection had detectable antibodies by about 21 days after symptoms first appeared. But the other half took longer.
Most guidelines suggest waiting at least 12 weeks after a potential exposure before taking a blood test. Testing earlier may catch some infections, but a negative result at two or three weeks doesn’t reliably rule anything out. If your first test is negative but you had a known exposure, retesting after the 12-week mark gives you a much more reliable answer.
Getting a Western Blot Confirmation
If your IgG screening test comes back with a low-positive index value and you want a definitive answer, the University of Washington Clinical Virology Lab offers the HSV Western blot. This test was developed at UW and remains the reference standard, though it has not been formally FDA-cleared. It requires a blood draw (a standard gold-top tube), and the sample needs to be frozen and shipped on dry ice if sent from an outside lab.
Your doctor can order the test directly, or you can contact the UW Clinical Virology Lab at 206-685-8037 for ordering instructions. Some clinicians aren’t familiar with this process, so you may need to bring up the option yourself. The test typically costs between $200 and $350 out of pocket, and not all insurance plans cover it.
Tests to Avoid
IgM antibody testing for herpes is still offered by some labs and providers, but it is not recommended for routine diagnosis. Unlike IgG tests, IgM tests cannot reliably distinguish between HSV-1 and HSV-2, and they can be positive during reactivations, not just new infections. This makes them unreliable for determining when you were infected or which type you carry. If a provider suggests an IgM test for herpes, ask for a type-specific IgG test instead.
Choosing the Right Test for Your Situation
- You have an active sore: Get a PCR swab as soon as possible, ideally while the lesion is still fresh. This gives you the most accurate result and identifies the virus type.
- You have no symptoms but want to know your status: Request a type-specific HSV-2 IgG blood test. Wait at least 12 weeks from any potential exposure. If the result falls in the low-positive range (1.10 to 3.50), pursue confirmatory testing with a Western blot before accepting the diagnosis.
- You had a negative blood test but recent exposure: Retest after 12 weeks. A single early negative test doesn’t rule out a new infection.
- You got a low-positive IgG result and want certainty: The University of Washington Western blot is the most definitive option available.
Standard STI panels at most clinics do not include herpes testing unless you specifically ask for it. If you want to be tested, you’ll need to request it by name. Specify that you want a type-specific IgG test for HSV-1 and HSV-2.