Short answer
Herpes testing depends heavily on whether there is an active sore, blister, ulcer, or rash to sample. When a lesion is present, CDC guidance favors type-specific virologic testing from the lesion, usually HSV NAAT or PCR when available. Blood tests look for HSV antibodies, not the virus itself, and they are not recommended as routine screening for everyone without symptoms.
The hard part is that HSV-1 and HSV-2 results do not always answer the question a person actually has. A swab can miss herpes if the lesion is old or not shedding virus. A blood test can be negative early after infection, HSV-1 antibodies do not prove the site of infection, and low-positive HSV-2 IgG results may need confirmation.
Common herpes test types
| Test type | Sample | What it can and cannot answer |
|---|---|---|
| HSV NAAT or PCR | Swab from a sore, blister, ulcer, or other lesion | Looks for HSV DNA and is generally the most sensitive lesion test. It can often identify HSV-1 versus HSV-2. |
| HSV viral culture | Swab from a lesion | Can confirm HSV from a lesion, but sensitivity drops as lesions heal and in recurrent disease. |
| Type-specific HSV IgG | Blood | Looks for antibodies to HSV-1 and/or HSV-2. It may help in selected situations but can be negative early and can be falsely positive, especially for low-positive HSV-2 results. |
| HSV IgM | Blood | CDC says IgM is not useful for HSV diagnosis because it is not type specific and can be misleading during recurrent episodes. |
| Type-common antibody test | Blood | Does not reliably distinguish HSV-1 from HSV-2, so it usually does not answer the most important counseling question. |
When a sore or blister can be swabbed
If a new genital or oral sore is present, timing matters. A fresh blister, ulcer, or moist lesion is usually more useful for HSV NAAT/PCR or culture than a dry, crusted, or healing lesion. MedlinePlus describes swab testing as collecting fluid and cells from a sore that has not begun to heal yet.
A negative swab does not always rule out herpes. CDC notes that viral culture sensitivity decreases rapidly as lesions heal, and failure to detect HSV from a lesion does not exclude infection because viral shedding is intermittent. If symptoms keep recurring, a clinician may recommend prompt repeat swabbing during the next fresh episode.
How HSV IgG blood tests fit in
Type-specific HSV IgG blood tests can be useful when there are recurrent or atypical genital symptoms with negative lesion tests, when a clinician made a diagnosis without lab confirmation, or when a sex partner has genital herpes. CDC says type-specific assays are based on glycoprotein G and should distinguish HSV-1 from HSV-2.
HSV blood tests need careful interpretation. CDC says HSV-2 antibody sensitivity varies and false-negative results can be more common early after infection, so repeat testing around 12 weeks after suspected acquisition may be considered. CDC also warns that one commonly used HSV-2 EIA can be falsely positive at low index values, and confirmatory testing with a different method, such as Biokit or Western blot, should be considered before interpreting a low-positive result as final.
HSV-1 IgG has a different limitation: many people acquired oral HSV-1 in childhood, and a positive HSV-1 antibody test does not tell whether infection is oral, genital, old, or recently acquired. That makes HSV-1 blood results especially easy to overinterpret if there are no matching symptoms.
Why routine screening is different
CDC recommends herpes testing for people with genital symptoms, but does not recommend herpes testing for people without symptoms in most situations. USPSTF recommends against routine serologic screening for genital herpes in asymptomatic adolescents and adults, including pregnant people.
The reason is not that herpes is unimportant. It is that the test result can create harm when it is disconnected from symptoms, exposure likelihood, test type, index value, and confirmatory testing. FDA has also reminded clinicians and laboratories that HSV-2 serologic tests can produce false reactive results, especially when used for general screening in lower-risk people.
Pregnancy and partner-history questions
Pregnancy deserves direct clinical guidance rather than casual self-interpretation. CDC pregnancy guidance says routine HSV-2 serologic screening of pregnant people is not recommended. However, type-specific serology may be useful in selected situations, such as counseling a pregnant person whose partner has known HSV infection.
Tell a clinician promptly about genital sores, blisters, burning, tingling, painful urination with lesions, a partner with genital herpes, or any suspected first episode during pregnancy. CDC notes that the risk to a newborn is highest when genital herpes is acquired near delivery, so timing and symptoms matter.
Questions to ask before testing
- Do I have a lesion that should be swabbed now, before it heals?
- Is the swab an HSV NAAT/PCR that reports HSV-1 versus HSV-2?
- If this is a blood test, is it type-specific HSV-1 and HSV-2 IgG?
- Was HSV IgM ordered, and if so, should it be ignored or repeated with a better test?
- If HSV-2 IgG is low-positive, what confirmatory test is available?
- If the result is negative, was testing done long enough after the possible exposure?
- What would this result change about treatment, disclosure, pregnancy planning, or partner testing?
- Should other causes of sores or symptoms be checked, such as syphilis, chancroid in rare settings, yeast, bacterial vaginosis, UTI, dermatitis, trauma, or mpox when clinically relevant?
FAQ
What is the best herpes test when sores are present?
CDC guidance says genital herpes lesions should be confirmed by type-specific virologic testing from the lesion, such as HSV NAAT/PCR or culture, when lesions are present. NAAT/PCR is generally the most sensitive test from a lesion sample.
Does CDC recommend routine herpes blood testing for everyone?
No. CDC does not recommend herpes testing for people without symptoms in most situations, and USPSTF recommends against routine serologic screening for genital herpes in asymptomatic adolescents and adults, including pregnant people.
Why can HSV-2 IgG blood tests be falsely positive?
CDC and FDA warn that HSV-2 serology can produce false reactive results, especially in low-risk people and with low-positive index values. Confirmatory testing may be needed before treating a low-positive HSV-2 blood result as a diagnosis.
Should HSV IgM be used to diagnose herpes?
CDC says HSV IgM testing is not useful because it is not type specific and can be positive during recurrent oral or genital episodes. A type-specific HSV-1 and HSV-2 IgG test is the relevant blood-test category when serology is appropriate.
Can a negative swab rule out herpes?
Not always. CDC notes that culture sensitivity decreases as lesions heal, and a negative test from an older lesion or absent lesion does not rule out HSV because viral shedding is intermittent.
What should pregnant people ask about herpes testing?
Pregnant people should tell a clinician about genital symptoms or a partner with genital herpes. CDC pregnancy guidance says routine HSV-2 serologic screening is not recommended, but type-specific serology may be useful in selected counseling situations.