Genital herpes is tested in two main ways: a swab of an active sore or a blood test that detects antibodies. Which test you get depends on whether you have visible symptoms at the time. A swab taken from a blister or ulcer is the most reliable method when lesions are present, while blood tests are used when no sores are visible or when you want to know your infection status between outbreaks.
Swab Testing During an Outbreak
If you have an active sore, blister, or ulcer, the preferred test is a swab. A clinician collects fluid or cells directly from the lesion and sends it to a lab. The standard method is a PCR test (which detects the virus’s genetic material), though viral culture is also used. PCR is more sensitive, meaning it catches more true positives, and it works better on sores that have already started healing.
Timing matters. A fresh, unbroken blister yields the best sample. Once a sore has crusted over or begun healing, the amount of virus drops significantly, and the test is more likely to come back negative even if herpes caused the lesion. If you notice a new sore, getting swabbed within the first 48 hours gives the most accurate result.
Swab tests can also tell you whether you have HSV-1 or HSV-2, which is useful information. HSV-1 genital infections tend to recur less frequently than HSV-2, so knowing the type helps you understand what to expect going forward.
Blood Tests for Herpes Antibodies
Blood tests don’t detect the virus itself. They detect antibodies your immune system produces in response to infection. This makes them useful when you have no active sores, when a swab came back negative but herpes is still suspected, or when a partner has been diagnosed and you want to know your own status.
The important distinction is between type-specific and non-type-specific tests. Type-specific tests identify antibodies that react to proteins unique to either HSV-1 or HSV-2, allowing the lab to tell you which type you carry. Non-type-specific tests lump both types together and are far less useful for clinical decisions. Current guidelines recommend only type-specific IgG tests for herpes serology.
You may also hear about IgM testing, which is sometimes marketed as detecting “recent” infection. IgM antibodies are not a reliable marker for new herpes infections. Studies have found IgM in roughly 30% of people with long-established HSV-2 infections, meaning a positive IgM result can’t distinguish a new infection from an old one. IgM testing for herpes is generally considered unreliable and is not recommended.
The Window Period
Blood tests require time to become accurate. After exposure, your body needs weeks to produce enough antibodies for a test to detect. The CDC notes that current tests can take up to 16 weeks or more to detect infection after exposure. Most people develop detectable antibodies within 2 to 12 weeks, but testing too early risks a false negative. If you had a recent exposure and your blood test is negative, retesting after the full window period gives a more reliable answer.
False Positives and Low-Positive Results
One of the trickiest parts of herpes blood testing is the false positive problem. Standard IgG tests report results as an index value, with anything at or above 1.1 considered positive. But research published in the Journal of Clinical Microbiology has consistently found that “low-positive” index values (between 1.1 and 3.0) are associated with a high rate of false positives. On one widely used testing platform, 38.7% of low-positive HSV-2 results in that range were falsely positive. For HSV-1, the false positive rate for low-positive values on that same platform reached 76.1%.
This means a result in the 1.1 to 3.0 range should not be taken at face value. Current guidelines recommend confirmatory testing for anyone with a low-positive HSV-2 result. The gold standard confirmatory test is the HSV Western Blot, offered through the University of Washington’s virology lab. A supplemental test called BioKit is another option. If your index value is above 3.5, the result is much more likely to be a true positive and may not require confirmation.
Why Routine Screening Isn’t Standard
If you’ve been to a clinic for STI testing, you may have assumed herpes was included in the panel. It typically is not. The CDC does not recommend routine HSV-2 blood testing for the general population, including asymptomatic pregnant women. The reasoning comes down to the false positive problem described above, combined with the psychological burden of a diagnosis that, in many cases, causes no symptoms.
Testing is recommended in specific situations: if you have recurrent or unusual genital symptoms, if a swab test was negative but herpes is still suspected, if you’ve had a clinical diagnosis without lab confirmation, or if a sexual partner has genital herpes. Clinicians may also consider testing for people presenting for an STI evaluation who have multiple sexual partners or who are living with HIV. If you want to be tested, you can request it, but you’ll likely need to ask specifically since it won’t be part of a standard screening panel.
Guidelines also recommend against routine HSV-1 blood testing. Because HSV-1 causes both oral and genital infections, a positive blood result can’t tell you where on your body the infection is. Someone with a history of childhood cold sores would test positive for HSV-1 antibodies, and that result says nothing about genital herpes.
At-Home Test Kits
Several companies now offer at-home herpes test kits, typically blood-based antibody tests that you collect via finger prick and mail to a lab. The lab technology behind these kits is generally the same as what a clinic uses. The concern is sample collection. Getting an adequate blood sample from a finger prick requires following instructions carefully, and a poor sample can compromise the result. As one physician at UAB Medicine noted, even experienced providers sometimes find it challenging to collect adequate swab samples, raising questions about whether self-collection at home matches clinic-quality specimens.
If you use an at-home kit, pay close attention to your index value if one is reported. A low-positive result (1.1 to 3.0) warrants follow-up with a clinician and potentially a confirmatory Western Blot, just as it would with any other blood test.
Which Test to Ask For
If you have an active sore, ask for a PCR swab. It’s the most accurate option and will tell you the virus type. If you have no symptoms but want to know your status, request a type-specific HSV-2 IgG blood test and make sure at least 12 to 16 weeks have passed since any potential exposure. If your result comes back in the low-positive range, ask about confirmatory testing with a Western Blot before accepting the diagnosis. Avoid IgM testing entirely, as it provides no clinically useful information for herpes.