The most common herpes test is called a PCR test (polymerase chain reaction), which detects the virus’s genetic material from a swab of an active sore. When no sores are present, the standard test is a type-specific IgG antibody blood test, which looks for your immune system’s response to the virus. These are the two primary ways herpes simplex virus (HSV) is diagnosed, though the specific test your provider orders depends on whether you have visible symptoms.
PCR Swab Test for Active Sores
If you have blisters or open sores, your provider will most likely order a nucleic acid amplification test, or NAAT. PCR is the most widely used form of NAAT. A healthcare professional uses a swab to collect fluid and cells from a herpes sore that hasn’t begun to heal yet. The test then searches that sample for genetic material from HSV-1 or HSV-2.
PCR is the preferred test because it’s both fast and highly sensitive. In head-to-head comparisons, PCR detects the virus in significantly more cases than the older method, viral culture. One study in the Journal of Clinical Microbiology found PCR had 100% sensitivity while culture caught only 50% of confirmed infections. PCR also identifies which type of herpes you have, HSV-1 or HSV-2, which matters for understanding your likely outbreak pattern and transmission risk.
Viral Culture
A viral culture is an older swab-based test that attempts to grow the virus from a sample taken from a sore. It’s less commonly used today because it misses infections far more often than PCR. Cultures work best on fresh, fluid-filled blisters. Once a sore starts crusting over or healing, the chance of a false negative climbs steeply. If your provider still uses viral culture, it can confirm infection when positive, but a negative result doesn’t reliably rule herpes out.
Type-Specific IgG Blood Test
When you don’t have any visible sores, the test used is a type-specific IgG antibody blood test. Instead of looking for the virus itself, this test detects antibodies your immune system produces in response to HSV infection. “Type-specific” means the test can distinguish between HSV-1 (typically oral herpes) and HSV-2 (typically genital herpes), which is important because the two types behave differently over time.
The key limitation is timing. After exposure, it can take up to 16 weeks or more for antibodies to reach detectable levels in your blood. If you test too soon after a potential exposure, you may get a false negative. For the most reliable result, wait at least 12 to 16 weeks after the encounter you’re concerned about.
IgG is the antibody type you want tested. An older test called IgM is sometimes still ordered, but it’s considered unreliable for herpes. IgM antibodies can cross-react between HSV-1 and HSV-2, can’t distinguish between a new infection and a reactivation, and produce frequent false positives. If you’re requesting herpes bloodwork, ask specifically for a type-specific IgG test.
Why Routine Screening Isn’t Standard
You might be surprised to learn that herpes blood testing is not part of standard STI panels. Most providers don’t screen for herpes unless you specifically ask, have symptoms, or have a known exposure. The reasoning is partly about test performance: IgG blood tests can produce false positives, particularly at low-positive index values, which creates anxiety without clear clinical benefit. The CDC does not recommend routine herpes screening for people without symptoms. If you want to be tested, you’ll typically need to request it directly.
Spinal Fluid PCR for Serious Cases
In rare situations where herpes is suspected of affecting the brain or spinal cord, doctors use a PCR test on cerebrospinal fluid (the liquid surrounding your brain and spine). This is collected through a spinal tap and is used to diagnose herpes encephalitis, a potentially life-threatening brain infection more commonly linked to HSV-1, or herpes meningitis, which is more often associated with HSV-2. This isn’t a test you’d encounter in a routine screening situation. It’s reserved for emergency settings when someone presents with severe neurological symptoms.
Which Test to Ask For
If you have an active sore or blister, ask for a PCR swab test. This gives the most accurate result and tells you which type of herpes you have. Timing matters: get swabbed as early as possible, ideally while the sore is still fresh and fluid-filled.
If you have no symptoms but want to know your status, ask for a type-specific HSV-1 and HSV-2 IgG blood test. Make sure it’s IgG, not IgM. Keep the 16-week window period in mind if you’re testing after a recent exposure. A negative result before that window closes may not be accurate.
If you’re unsure which test applies to your situation, simply telling your provider whether you currently have sores will guide them to the right one. The two approaches answer different questions: the swab confirms what’s causing a specific sore, while the blood test reveals whether you carry the virus at all.