Testing for HSV-2 depends on whether you currently have symptoms. If you have an active sore or blister, a swab test taken directly from the lesion is the most accurate option. If you have no visible symptoms, a blood test that detects antibodies is the primary method, though it comes with important accuracy limitations you should understand before ordering one.
Swab Testing: The Most Accurate Option
When you have an active genital sore, ulcer, or blister, a healthcare provider can swab the lesion and send the sample to a lab. Two types of swab tests exist: PCR (nucleic acid amplification) and viral culture. PCR is the preferred method because it directly detects viral DNA and is the most sensitive test available, with sensitivity ranging from 90.9% to 100% depending on the specific assay used. It also identifies whether you have HSV-1 or HSV-2.
Viral culture, the older method, grows the virus from the swab sample in a lab. It’s less sensitive than PCR, particularly for recurrent outbreaks, and its accuracy drops quickly as sores begin to heal. Some clinics still use culture when PCR isn’t available, but if you have the choice, PCR is the better test. For either swab method, timing matters. Get swabbed as early as possible in an outbreak, ideally when a sore is fresh and still fluid-filled, not after it has started crusting over.
Blood Tests: How They Work and Where They Fall Short
Blood tests don’t detect the virus itself. They look for antibodies your immune system produces in response to HSV-2 infection. The standard test is an IgG antibody test, which targets a specific protein on the virus’s surface called glycoprotein G. Because HSV-1 and HSV-2 each have a distinct version of this protein (gG-1 and gG-2), the test can distinguish between the two types.
The problem is accuracy. The CDC explicitly does not recommend routine herpes blood testing for people without symptoms, largely because the false positive rate is significantly higher than for other STI tests like chlamydia or gonorrhea. One study found the accuracy of HSV-2 IgG antibody testing was as low as 36% to 38% in certain populations, though other studies have reported accuracy closer to 70% to 83%. The wide range reflects differences in study populations and how “accuracy” is measured, but the takeaway is the same: a positive blood test result is not as reliable as many people assume.
Results come back as an index value. A value below 0.9 is negative, and above 1.1 is positive. Here’s the critical detail most people miss: index values between 1.1 and 3.0 carry a high risk of being false positives. In one large study, 56% of samples with index values under 3.0 that initially screened positive turned out to be false positives on confirmatory testing. If your result falls in this range, it needs further confirmation before you can trust it.
Why IgM Tests Are Unreliable
Some providers or at-home kits offer an IgM antibody test, which supposedly detects a “new” or “recent” infection. This test is not recommended for HSV-2 diagnosis. IgM antibodies are not specific to a recent infection. They can reappear during recurrences, cross-react between HSV-1 and HSV-2, and produce misleading results. If a provider orders an IgM test for herpes, it’s worth asking for an IgG test instead.
The Antibody Window Period
After exposure to HSV-2, your body needs time to produce detectable antibodies. Testing too soon will give you a false negative. Most people develop detectable antibodies within about two to four weeks, with a median detection time around 13 days in clinical studies. However, the range varies widely. Some people seroconvert in under a week, while others take over three months. About 80% of people with a new HSV-2 infection will test positive within four weeks of their first symptoms appearing.
If you already carry HSV-1, your body tends to produce HSV-2 antibodies faster (median of 8 days) compared to someone with no prior herpes exposure (median of 19 days). For the most reliable blood test result after a potential exposure, waiting at least 12 weeks gives the best chance of an accurate reading.
Confirmatory Testing With Western Blot
The Western blot is considered the gold standard for HSV antibody detection. It’s more specific than the standard IgG blood test, meaning it’s much better at correctly ruling out false positives. The CDC recommends confirmatory testing for anyone with an HSV-2 IgG index value between 1.1 and 3.0, and many clinicians also recommend it for any positive result that seems inconsistent with a patient’s history or risk level.
Western blot testing is not widely available at commercial labs. The University of Washington has historically been the primary reference lab offering this test. Your provider orders it, you get a blood draw, and the sample is sent to the specialized lab. It can take several weeks for results, and the test may cost more than a standard IgG since insurance coverage varies. Despite the inconvenience, if you received a low-positive IgG result and want certainty, this is the test that provides it.
At-Home Test Kits
Several companies sell at-home HSV-2 test kits that use a finger-prick blood sample mailed to a lab. These kits test for IgG antibodies, the same type of test you’d get at a clinic. When processed by a CLIA-accredited lab, the results are considered comparable to an in-office blood draw. The convenience and privacy are real advantages, but the same accuracy limitations apply. A low-positive result from an at-home kit still warrants confirmatory testing, just as it would from a doctor’s office. These kits also can’t replace a swab test during an active outbreak.
Which Test to Choose
Your situation determines the right test. If you have an active sore right now, request a PCR swab. This gives you the most accurate, type-specific diagnosis, and you should get tested as early in the outbreak as possible. If you have no symptoms but want to know your status after a potential exposure, an IgG blood test is your option, but wait at least 12 weeks after the exposure for the most reliable result.
If a blood test comes back positive with an index value between 1.1 and 3.0, treat that as inconclusive and pursue Western blot confirmation. If the index value is above 3.0, the result is more likely to be a true positive, though confirmatory testing is still reasonable if the result doesn’t match your clinical picture. A negative IgG test taken at least 12 weeks after exposure is generally reliable and doesn’t need confirmation.