If you have a new blister, ulcer, or sore, try to have it swabbed while it is still present. Ask whether the clinic can use a type-specific HSV nucleic-acid amplification test, usually called NAAT or PCR. This test looks for the virus in the lesion and can identify HSV-1 or HSV-2. 12
If you do not have a lesion, a type-specific blood test can sometimes help, but it answers a different question. It looks for antibodies showing previous HSV-1 or HSV-2 infection. It does not directly locate an infection: an HSV-1 result cannot tell whether infection is oral or genital, while CDC generally interprets a confirmed type-specific HSV-2 result as evidence of anogenital infection. Blood testing cannot tell when infection happened or who transmitted it, and testing too soon can produce a misleading result. 1237
US guidance does not recommend routine herpes blood screening for everyone without symptoms. That is not a prohibition on testing. Blood testing may still be useful when someone has had unexplained genital symptoms, received a visual diagnosis that was never confirmed, or has a partner with genital herpes. 124
The quickest way to choose a test
| Your situation | Most useful next step |
|---|---|
| You have a new blister, ulcer, or sore | Ask for a lesion swab using type-specific HSV NAAT/PCR. Go while the lesion is still fresh if you can. 12 |
| You had a lesion, but it is healing or gone | Ask whether direct testing is still useful and whether type-specific blood testing or evaluation for another cause makes sense. 16 |
| You have no symptoms but a partner has genital herpes | Discuss type-specific HSV-2 blood testing, its timing, and how a positive result would be confirmed. 12 |
| You recently had a possible exposure and have no lesion | You can seek advice now, but an early blood result may not settle the question. The timing section below explains the 12-week and 16-weeks-or-longer guidance. 123 |
| You received a positive HSV-2 blood result | Ask for the assay name, any numeric index value, and whether a different method was used for confirmation. 135 |
A swab and a blood test answer different questions
A lesion swab looks for HSV in the specific sore that was sampled. A blood test looks for the immune system's response to HSV somewhere in the body.
That difference determines what each test can tell you:
- A positive typed lesion test identifies HSV at the sampled site.
- A blood test can support previous infection with HSV-1 or HSV-2, but it does not locate the infection. This limitation is especially important for HSV-1 because the same virus can cause oral or genital infection.
- Neither test identifies the person who transmitted HSV or proves exactly when infection happened. 17
If you have a sore now, ask about a lesion PCR
When a genital blister, ulcer, fissure, or other suspicious lesion is present, CDC recommends type-specific testing from the lesion by NAAT or viral culture. NAAT is the more sensitive option and is often reported as PCR. The result should distinguish HSV-1 from HSV-2 because the type affects later counseling. 1
Go while the lesion is still present if you can. Viral culture becomes less sensitive as a lesion heals, and even a molecular test can miss HSV when a lesion is old or the sampled area is no longer shedding enough virus. Do not delay urgent care or treatment simply to preserve a testing opportunity. 12
Appearance alone is not always enough. Genital, anal, and perianal ulcers can have infectious and noninfectious causes. In US CDC guidance, evaluation includes HSV testing, syphilis testing, and HIV testing when HIV status is unknown. The exact evaluation depends on the person and local practice. 6
How to read a lesion result
HSV-1 or HSV-2 detected by NAAT/PCR: The test found that HSV type in the sampled lesion. This is direct evidence of HSV at that site.
HSV detected by a typed culture: A positive culture also identifies HSV in the lesion. A negative culture is less conclusive than a negative NAAT, especially when a lesion is recurrent or healing. 1
HSV not detected: The sample did not contain detectable HSV. This lowers the evidence for HSV in that lesion, but it does not always rule infection out. Lesion age, sample quality, and intermittent viral shedding matter. If symptoms recur, testing a fresh lesion may be more informative. 1
If you do not have a sore, decide what a blood test would clarify
CDC identifies three common situations in which type-specific HSV-2 antibody testing can help:
- recurrent or unusual genital symptoms with a negative lesion PCR or culture
- a clinical diagnosis of genital herpes that was never confirmed by a laboratory test
- a current or previous partner with genital herpes 12
These are targeted uses, not routine screening. Before testing, ask what a positive, negative, or unclear answer would change and what confirmation would be available if the result were reactive.
Is herpes included in a “full STI panel”?
Not necessarily. Herpes blood testing may or may not be included when someone asks to be tested for “everything.” Ask which infections are included and whether any HSV test is a lesion NAAT, type-specific antibody test, or another method. 2
Which blood test should I ask about?
Ask whether the test is type-specific, meaning it reports HSV-1 and HSV-2 separately. Many current antibody tests are described as type-specific IgG tests. A result that reports only “HSV antibody” without separating the types is less useful. 1
HSV IgM should not be used to decide whether infection is new. CDC does not recommend it because available IgM tests are not type-specific and can be positive during recurrent oral or genital episodes. 1
When after exposure can a blood test help?
There is no single day on which every HSV blood test becomes conclusive. Antibodies take time to develop, and people and assays do not all become positive at the same point.
Two current CDC statements are relevant:
- The clinical guideline says to repeat type-specific HSV-2 antibody testing 12 weeks after the presumed time of recent acquisition.
- The patient testing page says it can take 16 weeks or longer after exposure for current tests to detect infection. 12
These statements are different, and the sources do not explain the difference. The practical conclusion is not to choose one as a guaranteed cutoff:
- If a lesion appears at any point, seek a swab then. Do not wait for the blood-testing window.
- A negative blood result soon after exposure may be too early. Record the exposure date and test date.
- At about 12 weeks, repeat type-specific HSV-2 testing may be appropriate after suspected recent acquisition. This is the repeat point in CDC's clinical guidance.
- If a 12-week result is negative but a later answer still matters, ask whether testing at 16 weeks or later would add useful information. CDC's patient guidance warns that detection can take that long or longer.
A negative result at either point should be interpreted with the test used, the reason for testing, and any symptoms. A positive result cannot prove that a recent event caused the infection; it may reflect an older infection that had never been tested. 127
What the main blood-test results can and cannot establish
| Result | What it can support | What it does not establish |
|---|---|---|
| HSV-1 antibody positive | Previous HSV-1 infection | Oral versus genital site, timing, source, or current shedding 1457 |
| HSV-2 antibody positive and appropriately confirmed | Previous HSV-2 infection; CDC generally interprets type-specific HSV-2 antibody as evidence of anogenital infection | The site of a past lesion, timing, source, current shedding, or future symptom pattern 137 |
| HSV-1 or HSV-2 antibody negative | No antibody was detected by that assay at that time | A definitive rule-out when testing was early; current HSV-1 assays can also miss established infection 125 |
| Equivocal or indeterminate | The assay did not produce a clear positive or negative answer | A diagnosis; the appropriate repeat or confirmation step depends on the assay and timing 135 |
A positive HSV-1 blood result
HSV-1 can cause oral or genital infection. A positive blood result does not show which site is involved. It should not be treated as proof of genital HSV-1 when no genital lesion has tested positive. Current HSV-1 antibody assays can also miss some established infections. When genital HSV-1 is suspected and a lesion is present, testing the lesion is the better way to establish the site and type. 145
A positive HSV-2 blood result
CDC generally interprets type-specific HSV-2 antibody as evidence of anogenital infection. This interpretation is strongest when the result has been confirmed when confirmation is indicated. The blood sample itself does not identify a past lesion site, when infection happened, who transmitted it, or whether virus is being shed today. 17
A negative blood result
A negative result means that the assay did not detect antibodies at that time. It can be too early after a recent exposure, and HSV-1 antibody tests can miss some established HSV-1 infections. If timing was early or symptoms continue, review the assay, dates, and next useful testing opportunity with a clinician. 125
How a low-positive HSV-2 result is assessed
A reactive HSV-2 screening result near the assay's cutoff is not automatically a confirmed diagnosis. False-reactive results occur more often when testing is done too soon, when the person tested had a lower likelihood of infection before testing, or when the result is close to the cutoff. 3
Some assays report a numeric index value. CDC specifically warns that the HerpeSelect HSV-2 EIA is often falsely positive at index values from 1.1 to 3.0 and recommends confirmation with a different method, such as Biokit or Western blot, before interpretation. That numeric range is specific to HerpeSelect and should not be applied automatically to every HSV-2 test. 1
A 2024 comparison with University of Washington Western blot found meaningful performance differences among three automated HSV IgG platforms. The FDA's broader advice is to use confirmatory testing for reactive HSV-2 results as directed by the assay's labeling and professional guidance. 35
If your HSV-2 blood test is reactive, ask:
- What is the assay or platform name?
- Does the report include a numeric index value?
- Is the result considered low or near the cutoff for that assay?
- Was confirmation performed with a different method?
- If confirmation is unavailable, what uncertainty remains?
An index value helps interpret that assay. It is not a clock and does not show whether HSV is being shed today. 137
What if the swab is negative but symptoms continue?
First check which test was used and when the sample was taken. A negative culture from a healing lesion is less conclusive than a negative NAAT from a fresh lesion. Even a negative NAAT does not exclude HSV in every case. 1
If another fresh lesion appears, prompt repeat sampling may provide a better specimen. Type-specific blood testing may also help when recurrent or unusual genital symptoms continue after a negative lesion test. At the same time, other causes should remain open rather than assuming every genital symptom is herpes. 16
The best next step depends on the appearance and location of the symptoms, the original test, timing, other possible infections, pregnancy, and immune status. That is an individualized clinical decision.
Why routine blood screening is not recommended for everyone
The US CDC and USPSTF recommend against routine serologic screening for genital herpes in the asymptomatic general population. Their reasons include false-positive results in lower-likelihood populations, limitations of current tests, and the USPSTF's conclusion, with moderate certainty, that the harms of screening everyone outweigh the benefits. 1234
This is a screening recommendation, not a rule that symptom-free people must never be tested. Targeted blood testing may still be useful after past unexplained symptoms, an unconfirmed clinical diagnosis, or a partner's diagnosis. The decision should begin with the question the test is meant to answer. 12
Tests and shortcuts that do not settle the question
HSV IgM
HSV IgM is not recommended for routine diagnosis and cannot establish that an infection is new. 1
A random genital swab when no lesion is present
CDC does not recommend a blind genital swab to rule out HSV. Shedding is intermittent, so a negative random sample is not a reliable exclusion. 1
HSV PCR on blood for ordinary genital herpes
Blood PCR is not the routine test for genital herpes. CDC reserves it for situations in which disseminated infection is a concern. Suspected infection involving the brain, a newborn, or other organs follows a different diagnostic pathway. 1
Appearance alone
Some lesions look characteristic, but clinical appearance can be wrong. When a lesion can be sampled, laboratory confirmation gives more reliable information. 16
A mail-in result without its method
Do not assume that an online or mail-in result is definitive or useless based only on where the sample was collected. Obtain the laboratory and assay name, whether HSV-1 and HSV-2 were reported separately, any numeric index value, and the confirmation policy. Direct-to-consumer services were not individually assessed for this guide.
When you need individualized medical advice
Seek care rather than relying only on this general timeline when:
- you have a new blister, ulcer, or painful lesion that can be examined and sampled 1
- you are pregnant and have new genital symptoms or a possible new exposure, especially in the second half of pregnancy 1
- you have significant immune suppression or unusually severe or atypical lesions 1
- a baby may have been exposed to HSV during delivery 1
- you have eye pain, worsening eye redness, light sensitivity, or a change in vision 8
Routine HSV-2 blood screening is not recommended for every asymptomatic pregnant person. That does not mean pregnancy-related symptoms or exposure should wait. CDC says targeted type-specific testing can sometimes help assess risk and guide counseling, including when a pregnant person has a partner with HSV. Possible acquisition in the second half of pregnancy needs specialist obstetric and infectious-disease management. 147
Eye, neonatal, brain, and disseminated HSV use different and sometimes urgent diagnostic pathways. The Symptoms guide gives specific urgent-care boundaries; use an appropriate local urgent or emergency service rather than waiting for an online answer when the situation appears urgent. This testing guide does not cover those protocols. 18
Questions to take to a clinician or laboratory
- Can this lesion be swabbed today?
- Is the lesion test an HSV NAAT/PCR or viral culture?
- Will it report HSV-1 and HSV-2 separately?
- What specific question would a blood test answer in my situation?
- Is the blood test type-specific IgG?
- What is the assay name and, if applicable, the numeric index value?
- If HSV-2 is reactive or near the cutoff, what different-method confirmation is available?
- Was my test taken too early to treat a negative result as final?
- If the result is negative or unclear, what should happen if a new lesion appears?
- Should another cause, including another infection, be evaluated?
Evidence and sources
Evidence last checked: 6 September 2026
Evidence scope: Current US CDC genital-herpes and genital-ulcer guidance, CDC patient testing information, the 2023 FDA false-reactive HSV-2 warning, the 2023 USPSTF screening recommendation, and a 2024 peer-reviewed comparison of automated HSV IgG assays.
Important limitations: Test availability, index reporting, and confirmation pathways vary by country and laboratory. The checked sources do not provide one assay-independent rule for every reactive result. Direct-to-consumer services were not individually audited. CDC's 12-week clinical repeat point and 16-weeks-or-longer patient guidance are both preserved because neither source establishes a universal cutoff.
Sources
- CDC. Sexually Transmitted Infections Treatment Guidelines, 2021: Genital Herpes (opens in a new tab)Return to citation
- CDC. Screening for Genital Herpes (opens in a new tab)Return to citation
- US Food and Drug Administration. HSV-2 Tests for Genital Herpes Can Produce False Reactive Results (opens in a new tab)Return to citation
- US Preventive Services Task Force. Genital Herpes Infection: Serologic Screening (opens in a new tab)Return to citation
- Crawford KHD, et al. Performance characteristics of highly automated HSV-1 and HSV-2 IgG testing (opens in a new tab)
DOI: 10.1128/jcm.00263-24
Return to citation - CDC. Diseases Characterized by Genital, Anal, or Perianal Ulcers (opens in a new tab)Return to citation
- CDC. About Genital Herpes (opens in a new tab)Return to citation
- NHS. Herpes simplex eye infections (opens in a new tab)Return to citation