Herpes is diagnosed through two main approaches: swab tests taken from an active sore, or blood tests that detect antibodies. The right test depends on whether you currently have visible symptoms. Getting the wrong test, or testing too early, can lead to misleading results.
Swab Tests for Active Sores
If you have a blister, ulcer, or any suspicious lesion, a swab test is the most reliable way to confirm herpes and identify whether it’s HSV-1 or HSV-2. A clinician collects fluid or cells from the sore using a swab, then sends it to a lab for analysis. Two types of swab tests exist, and the difference in accuracy between them is significant.
PCR (nucleic acid amplification testing): This is the preferred method. PCR detects the virus’s genetic material directly and is highly sensitive and specific. In head-to-head comparisons, PCR catches 100% of positive samples, making it far more reliable than the older alternative. It works well even on sores that have started to crust over or heal, though fresher lesions still give the best results.
Viral culture: The traditional test, still used in some clinics where PCR isn’t available. A sample is placed in a lab dish to see if the virus grows. The problem is sensitivity: culture detects only about 50% of true positives in comparative studies. Its accuracy drops further with recurrent outbreaks and older lesions. If culture is the only option, getting swabbed as early as possible during an outbreak improves the odds of a correct result.
Timing matters with both swab methods. A negative swab doesn’t rule out herpes, because the virus sheds intermittently. Swabbing skin that has no visible lesion is not recommended for diagnosis since the chance of catching the virus on a random day is low.
Blood Tests for Antibodies
Blood tests look for antibodies your immune system produces in response to herpes infection. They’re useful when you have no active sores but want to know your status, or when a swab test came back negative despite suspicious symptoms. The key detail: you need a type-specific IgG test, one that distinguishes between HSV-1 and HSV-2. Older tests that lump both types together are not informative enough to guide decisions.
The most widely used screening test is the HerpeSelect HSV-2 IgG assay. It reports results as an index value. A value below 0.90 is negative, and above 1.10 is considered positive. But there’s a well-known gray zone. Results between 1.10 and 3.50 have a meaningful chance of being false positives, and the CDC recommends confirmatory testing for anyone whose score falls in that range. Even among clearly false-positive results, about 20% had index values above 3.50, so no single cutoff is perfect.
One important limitation of HSV-1 blood testing: a positive result doesn’t tell you whether the infection is oral or genital. Most HSV-1 infections are oral (cold sores), so a positive HSV-1 antibody result in someone concerned about genital herpes may not answer the question they’re actually asking.
The Window Period
Antibodies take time to develop after exposure. Current blood tests can take up to 16 weeks or more to detect a new infection. Testing too soon after a potential exposure risks a false negative. If your initial test is negative but you had a recent exposure, retesting after the window period gives a more reliable answer. Swab tests don’t have this limitation since they detect the virus itself, not your immune response to it.
Tests You Should Avoid
Not all herpes tests are created equal, and some are actively discouraged by clinical guidelines.
- IgM blood tests: These are not type-specific, meaning they can’t distinguish HSV-1 from HSV-2. They can also turn positive during recurrent outbreaks, not just new infections, so they don’t reliably indicate when you were infected. The CDC explicitly recommends against IgM testing for herpes.
- Tzanck preparation: An older method where cells from a lesion are examined under a microscope for characteristic changes. It’s insensitive and nonspecific, meaning it misses many true cases and can falsely suggest herpes when something else is causing the sore.
- Direct immunofluorescence: Uses fluorescent-labeled antibodies to look for viral proteins in a sample. It lacks the sensitivity of PCR or even culture and is not recommended.
Confirmatory Testing With Western Blot
If a blood test result is ambiguous, particularly an index value in the 1.10 to 3.50 range, the gold standard confirmatory test is the HSV Western Blot. This test is processed at the University of Washington’s virology lab, one of the few facilities that offers it. You can order a test kit by calling 1-800-713-5198 or through their lab website. Your clinician draws blood locally and ships the sample. The Western Blot is considered the most accurate serologic test available and is used to settle uncertain results from standard screening assays.
When Screening Is and Isn’t Recommended
Routine herpes blood testing for people without symptoms is not recommended. The U.S. Preventive Services Task Force gives population-wide screening a “D” grade, concluding with moderate certainty that the harms of screening (primarily false positives and the psychological distress they cause) outweigh the benefits in asymptomatic people. This applies to adolescents, adults, and pregnant individuals without symptoms or known history.
Blood testing is considered useful in specific situations: recurrent or unusual genital symptoms with a negative swab result, a clinical diagnosis that was never lab-confirmed, or when a sexual partner has known genital herpes. People living with HIV or other immune-suppressing conditions fall outside the general screening recommendation and may benefit from testing.
What Testing Costs
Costs vary depending on insurance coverage and where you go. Labcorp’s direct-to-consumer HSV-1 and HSV-2 antibody test is listed at $149 without insurance. Many sexual health clinics, including Planned Parenthood locations, offer testing on a sliding fee scale. PCR swab tests ordered through a provider’s office are typically covered by insurance when there’s a clinical reason for the test, such as an active lesion. The Western Blot confirmatory test is generally an out-of-pocket expense and tends to cost more than standard blood panels.
Choosing the Right Test
The decision tree is straightforward. If you have an active sore, get a PCR swab. It’s the most accurate test available for symptomatic herpes, and it tells you the virus type. If you have no symptoms but want to know your status for a specific reason, request a type-specific IgG blood test and make sure at least 16 weeks have passed since any potential exposure. If your blood test comes back with a low-positive index value, ask about confirmatory testing with the Western Blot before drawing conclusions. And skip the IgM test entirely, regardless of what’s offered.