How to test for herpes: swab, blood test and false positives

To test for herpes, a clinician swabs a sore and a lab checks it for the virus, or a blood test looks for antibodies to HSV-1 and HSV-2. The swab is more accurate, but it needs a sore that hasn't started to heal. Without a sore, CDC recommends a blood test only in certain cases, because false positives are common in people at low risk. For prices from every provider we track, see our herpes test page.

Key points

• A swab of a fresh sore, tested with a NAAT such as PCR, is the most sensitive herpes test, and it tells HSV-1 from HSV-2.
• Blood tests look for type-specific IgG antibodies, which can take up to 16 weeks or more to show up.
• CDC and the U.S. Preventive Services Task Force don't recommend herpes blood tests for people without symptoms, including in pregnancy.
• Low positive HSV-2 results are often false. A second test with a different method checks them.
• Every at-home herpes kit we track goes to a lab, and some check HSV-2 only.

Swab test or blood test?

Swab of a sore (PCR or NAAT)

If you have a blister or sore, see a clinician while it's fresh. CDC says swab tests work best on a sore that isn't crusted over or healing. It calls NAAT, the family of tests that includes PCR, the most sensitive herpes test. Viral culture, an older option, misses more infections, especially as a sore heals. The lab reports HSV-1 or HSV-2, which matters because CDC says genital HSV-2 comes back much more often than genital HSV-1.

A negative swab doesn't rule herpes out, because the virus isn't shed all the time. CDC also says swabbing the genitals when there's no sore shouldn't be used to diagnose herpes.

Blood test (type-specific IgG)

A herpes blood test looks for antibodies to HSV-1 and HSV-2, not for the virus. CDC says these antibodies develop in the first weeks after infection and last for life. Ask for a type-specific IgG test, which tells the two types apart. CDC says IgM tests aren't useful, because they can't tell the types apart and might be positive during a recurrence of oral or genital herpes.

So does herpes show up in a blood test? Yes, once antibodies have formed. CDC notes that the test can't show when you got herpes or who gave it to you.

Testing is the same for women and men. CDC says a clinic's test for "everything" may not include herpes, so ask.

How accurate is a herpes blood test?

CDC puts the sensitivity of type-specific HSV-2 tests at 80% to 98%, so they miss some infections, more often early on. False positives are the bigger problem. CDC says the most widely used HSV-2 test, HerpeSelect, is often falsely positive at low index values, from 1.1 to 3.0. The index is the number the test reports.

What can cause a false positive herpes test?

In 2023 the FDA warned labs and clinicians about false positive HSV-2 blood tests. Citing CDC, it says a wrong result is more likely when a person:

• has a low risk of infection
• gets a result near the cutoff, called a low positive
• tests too soon after infection

CDC says positive results from these tests, especially low ones, should be checked with a second test that uses a different method, such as the Biokit or Western blot. Quest says that when its HSV-2 result is above 1.09, the lab runs a confirmatory test on the same sample at no extra cost. myLAB Box says it doesn't offer the Western blot. If your test doesn't include confirmation, talk to a clinician before you act on a low positive.

Who should get a herpes blood test?

CDC recommends herpes testing for people with genital symptoms, but not for most people without them, because of the test's limits and the chance of a wrong result. The U.S. Preventive Services Task Force gives routine blood screening a "D" grade, meaning it recommends against screening people without symptoms, including pregnant people.

CDC says a blood test might be useful if:

• you have genital symptoms that could be herpes, including sores that come back while swab tests stay negative
• you have, or had, a partner with genital herpes
• a clinician found signs of herpes that still need confirming

Can you test for herpes without an outbreak?

Yes, with a blood test, because antibodies stay in the blood between outbreaks. A swab needs a sore. If a sore heals before anyone tests it, get the next one swabbed early.

When to test after an exposure

CDC's treatment guidelines say to repeat the blood test 12 weeks after a possible recent exposure. Its testing page says current tests can take up to 16 weeks or more to detect an infection. So test from 12 weeks, and trust a negative result most from 16 weeks. Our window periods guide and when-to-test calculator cover other infections.

HSV-1 and HSV-2: what a result means

HSV-2. CDC says nearly all HSV-2 infections are sexually acquired, so a confirmed result points to herpes in the genital or anal area, even without symptoms.

HSV-1. These antibodies are common. In CDC's national survey for 2015 to 2016, 47.8% of people aged 14 to 49 had HSV-1 antibodies and 11.9% had HSV-2. CDC says most people with oral herpes got it in childhood or young adulthood, through non-sexual contact with saliva. HSV-1 can also cause genital herpes through oral sex, but CDC says an HSV-1 blood test typically shouldn't be used to diagnose genital herpes. A swab of a genital sore confirms it.

Negative. No infection, or a test taken too early.

Do they test for herpes when you're pregnant?

Not routinely. CDC's guidelines say routine HSV-2 blood screening isn't recommended in pregnancy, and the Task Force recommends against it. Instead, CDC says every pregnant woman should be asked about past genital herpes or symptoms, and checked for symptoms and sores when labor starts. A blood test might be offered to a woman who has never had genital herpes and whose partner has herpes. If you have herpes, tell your prenatal care provider. CDC says you may need medicine toward the end of pregnancy.

At-home herpes tests

Every at-home herpes test we track is a kit you mail to a lab. We found no herpes self-test that gives a result at home.

• LetsGetChecked. A finger-prick blood sample, tested for HSV-1 and HSV-2 antibodies, with results about 2 to 5 days after the lab receives it.
• myLAB Box. A finger-prick sample tested for HSV-2 antibodies only. It suggests retesting in about 3 months if the infection may be recent.
• Wisp. A swab of an active sore, tested for HSV-1 and HSV-2, with results 3 to 5 business days after the lab receives it. Its 9-panel kit also tests for HSV-1 and HSV-2.

A home blood test has the same window period and false positives as a blood draw at a lab.

Rows marked "HSV-2 only" cover part of the test. Our at-home STD tests guide compares kits for other infections.

How much does a herpes test cost?

Current prices for a test of both HSV-1 and HSV-2, across the providers we track:

Our herpes test page lists every offer, including lab visits and panels. A swab of a sore needs a visit to a clinician, so its cost depends on the clinic and your insurance. Our STD test cost guide covers insurance and free clinics.

If your result is positive

Genital herpes is common, and CDC says it can be treated. There's no cure, but medicine can prevent or shorten outbreaks, and a daily medicine makes it less likely you'll pass herpes to a partner. Get a low positive HSV-2 result confirmed first.

CDC recommends an HIV test for everyone with genital herpes. It also advises telling current partners, and future partners before sex. A type-specific blood test can show a partner whether they already have the virus. Our positive result guide covers treatment and talking with partners.

Privacy

Herpes isn't on CDC's list of nationally notifiable conditions. Testing is still confidential, not anonymous. Our privacy guide explains what ends up in your records.