Herpes testing typically involves one of two approaches: a swab test taken from an active sore, or a blood test that detects antibodies your immune system has built against the virus. Which test you need depends on whether you currently have symptoms. A swab during an active outbreak is the most reliable route, while blood tests are useful when no sores are present but require careful timing and interpretation.
Swab Tests During an Active Outbreak
If you have a visible sore, blister, or ulcer, a swab test is the most straightforward and accurate option. A clinician collects a sample directly from the lesion and sends it to a lab. Two types of swab tests exist, and one is significantly better than the other.
PCR testing (which detects the virus’s genetic material) is now considered the gold standard. In comparative studies, PCR detected herpes in 85.7% of confirmed cases while viral culture caught only 42.9%. When analyzed head to head, PCR reached 100% sensitivity compared to 50% for culture. PCR also picks up the virus from lesions that are starting to heal, when viral culture often comes back negative because there isn’t enough live virus left to grow in a lab dish. Overall, PCR sensitivity for lesion specimens runs between 80% and 90%, though this varies by laboratory.
Viral culture, the older method, is still used at some clinics. It works best on fresh, fluid-filled blisters sampled within the first 48 hours. Once a sore starts crusting over, viral culture becomes unreliable. If your provider offers a swab test, it’s worth asking whether they’re sending it for PCR rather than culture.
Both swab methods can also tell you whether you have HSV-1 or HSV-2, which matters for understanding your likely recurrence rate and transmission risk.
Blood Tests When No Sores Are Present
If you don’t have an active outbreak, a blood test is the main option. These tests don’t look for the virus itself. Instead, they detect IgG antibodies, proteins your immune system produces in response to herpes infection that remain in your blood permanently. Most labs use a type-specific IgG test that can distinguish between HSV-1 and HSV-2.
The critical detail with blood tests is timing. After a new infection, it can take 3 to 6 months for IgG antibodies to reach detectable levels. If you were exposed recently and test too early, you could get a negative result even though you’re infected. Antiviral medication can delay antibody development further. For the most reliable result, wait at least 12 weeks after a possible exposure before testing, and ideally longer if your initial result is negative but you still have concerns.
False Positives and the Low-Positive Problem
Blood tests for HSV-2 have a well-known weak spot: false positives. The test reports a numerical index value, with anything at or above 1.1 considered positive. But many results in the lower positive range don’t hold up when checked with a more precise method.
Quest Diagnostics, one of the largest testing labs in the U.S., flags any HSV-2 IgG result between 1.1 and 6.0 for automatic confirmatory testing because false positives cluster in that range. If your HSV-2 blood test comes back positive with an index value in that zone, the result should not be treated as definitive without a second test to confirm it.
The most trusted confirmatory test is the Western Blot developed at the University of Washington. It requires a blood draw sent to their lab specifically. Your provider can order it, or you can contact the University of Washington Clinical Virology Lab for instructions. This test is not FDA-cleared (it was developed and validated in-house), but it is widely regarded by specialists as the most accurate way to resolve an uncertain result.
Why IgM Tests Are Unreliable
Some providers still order an IgM blood test, sometimes telling patients it can identify a “new” infection. This is misleading. IgM antibodies were once thought to appear only during a first infection and then disappear, but research has shown that’s not how herpes works. IgM shows up in about a third of people during recurrent outbreaks, long after their initial infection. At the same time, IgM tests miss up to half of people with a genuinely new infection confirmed by swab testing.
A positive IgM result can’t tell you when you were infected, and a negative one can’t rule out a recent exposure. If a provider suggests an IgM test for herpes, ask for a type-specific IgG test instead.
Testing Without Symptoms
You might wonder whether you should get a blood test even if you’ve never had symptoms. The CDC specifically recommends against routine herpes screening for people without symptoms in most situations. The reasoning comes down to the false positive problem: in a low-risk person with no symptoms, a positive blood test is more likely to be wrong than in someone with a clinical reason to test. A false positive creates significant anxiety over an infection that isn’t there.
No major medical organization recommends routine screening in asymptomatic adults, adolescents, or pregnant women. Testing makes the most sense when you have symptoms, a partner with a known diagnosis, or a specific exposure you’re concerned about.
Can You Test for Viral Shedding?
Herpes can shed from the skin without causing visible sores, which is how many transmissions happen. You might wonder if there’s a way to test for this. Technically, PCR swabs can detect asymptomatic shedding. In one study of pregnant women swabbed daily, PCR detected shedding on 13.8% of days compared to just 2.3% with culture. But shedding is intermittent and unpredictable. A negative swab today doesn’t mean you won’t shed tomorrow. Daily swabbing isn’t practical or recommended outside of research settings, so there’s no useful clinical test for asymptomatic shedding at this time.
Which Test to Ask For
- Active sore present: PCR swab of the lesion. This gives the fastest, most accurate answer and identifies the virus type.
- No sore, but possible exposure more than 12 weeks ago: Type-specific HSV IgG blood test. Make sure it distinguishes HSV-1 from HSV-2.
- Low-positive HSV-2 blood result (index 1.1 to 6.0): Request confirmatory testing, ideally the University of Washington Western Blot.
- Recent exposure, under 12 weeks ago: Wait and retest. Antibodies may not be detectable yet.
Many clinics, sexual health centers, and online lab ordering services offer herpes testing. If you’re ordering through a provider, specify that you want a type-specific IgG test and not an IgM test. If your result falls in the ambiguous low-positive range, push for confirmatory testing before drawing conclusions.