Lab result explainedInflammationLast updated November 11, 2026

HSV IgG test: herpes blood test results, HSV-1 and HSV-2 index values, and false positives

HSV IgG (herpes blood test) (HSV IgG) · HSV-1 and HSV-2 type-specific IgG (glycoprotein G) serology · reported in Index value (sample signal divided by calibrator), reported separately for HSV-1 IgG and HSV-2 IgG; some labs report simply negative, equivocal or positive

The HSV IgG test is a blood test for antibodies to herpes simplex virus, reported separately for HSV-1 and HSV-2 as an index value: below 0.90 is negative, 0.90 to 1.09 equivocal, and 1.10 or above positive on the most widely used assay. It tells you whether you have ever been infected with each type, because IgG antibody persists for life, but it cannot tell you where the infection is (mouth or genitals), when you acquired it, or whether you are currently shedding virus. Antibodies take 3 to 12 weeks to appear, occasionally longer.

Herpes is common and mostly silent. In the United States about 48 percent of 14- to 49-year-olds have HSV-1 antibodies and about 12 percent have HSV-2, and roughly 9 in 10 people with HSV-2 antibodies have never been diagnosed. HSV-1 usually means oral infection acquired in childhood, but it now causes about half of new genital herpes in young adults, so a positive HSV-1 result is genuinely ambiguous. HSV-2 almost always means genital infection.

The test's main weakness is the low-positive HSV-2 result. Index values between 1.10 and about 3.0 are confirmed by the reference Western blot only about half the time in people without symptoms or risk factors, while values above 3.5 are almost always real. Because of these false positives, the lack of proven benefit and the distress a result can cause, the CDC and the US Preventive Services Task Force recommend against routine herpes blood testing in people without symptoms; it is most useful when there are recurrent genital symptoms with negative swabs, a partner with known herpes, or HIV.

HSV IgG at a glance

  • What it is: a blood test for IgG antibodies to HSV-1 and HSV-2, using the type-specific glycoprotein G proteins; reported as an index value for each type.
  • Normal (negative): index below 0.90 for both types. Conclusive only 12 to 16 weeks after the last possible exposure, since antibodies take weeks to form.
  • Positive: index 1.10 or higher. HSV-2 positive almost always means genital herpes, past or present. HSV-1 positive means oral or genital infection and cannot say which; about half of adults are positive.
  • Low positive HSV-2 (1.10 to 3.0, some labs say 3.5): roughly half are false positives in people without symptoms; ask for a confirmatory Western blot or a second different assay before accepting the result.
  • Equivocal (0.90 to 1.09): neither positive nor negative; repeat in 2 to 4 weeks or confirm with a different test.
  • Next step: a sore is tested by PCR swab, not by blood; a positive blood test without symptoms is a conversation about transmission risk, not a reason for treatment on its own.

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What HSV IgG measures

HSV-1 and HSV-2 share most of their proteins, so older antibody tests could not tell them apart. Type-specific tests use glycoprotein G, which differs between the two viruses (gG1 and gG2), to measure IgG antibodies to each separately. The result is expressed as an index: the signal from your sample divided by a calibrator, so 1.0 is the cutoff, not a concentration. Index values are not interchangeable between laboratories or assays and do not measure how much virus you carry or how infectious you are; a 1.5 and a 6.0 are both simply positive.

IgG appears 2 to 12 weeks after infection, with a median of about 3 to 4 weeks for HSV-2 on enzyme immunoassays, and most people are positive by 12 weeks; a small minority take 16 weeks or longer. Once formed, IgG persists for life, so the test detects past infection whether or not you have ever had a symptom. IgM testing is not recommended by the CDC: it is not type-specific, is often positive during recurrences rather than only in new infection, and has a high false-positive rate, so an isolated positive IgM means little.

Performance differs by type. For HSV-2, the common enzyme immunoassays are 80 to 98 percent sensitive and about 96 percent specific, but in low-prevalence populations that specificity translates into many false positives at low index values. For HSV-1, the same assays miss up to 30 percent of true infections, so a negative HSV-1 result is less reliable than a negative HSV-2 result. The University of Washington Western blot is the reference test, with sensitivity and specificity above 97 percent, and is used to confirm low-positive or discordant results. For an active sore, a PCR swab of the lesion is more accurate than any blood test and also gives the type.

Normal range for HSV IgG

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (Index value (sample signal divided by calibrator), reported separately for HSV-1 IgG and HSV-2 IgG; some labs report simply negative, equivocal or positive)Notes
HSV-1 or HSV-2 IgG index below 0.90NegativeNo antibody detected. Conclusive if more than 12 to 16 weeks have passed since the last possible exposure. A negative HSV-1 result is less reliable than a negative HSV-2 result because the assay misses up to 30 percent of HSV-1 infections. Cutoffs differ slightly between assays.
Index 0.90–1.09EquivocalNeither positive nor negative. Repeat in 2 to 4 weeks (a true early infection will rise) or confirm with a Western blot or a different assay.
HSV-2 IgG index 1.10–3.0 (some labs use 3.5)Low positiveIn people without genital symptoms or a known exposure, only about 40 to 50 percent of results in this band are confirmed by Western blot. Confirmation is recommended before accepting the diagnosis.
HSV-2 IgG index above 3.0–3.5High positivePositive predictive value above 90 to 95 percent; almost always true HSV-2 infection, usually genital, whether or not you have had symptoms.
HSV-1 IgG index 1.10 or abovePositivePast or present HSV-1 infection; about half of US adults are positive. Cannot distinguish oral from genital infection; a higher index does not mean genital. Low-positive HSV-1 values are also sometimes false.
Both HSV-1 and HSV-2 positivePositive for both typesCommon in people with HSV-2, since most adults also carry HSV-1. Prior HSV-1 makes a new HSV-2 infection milder and makes HSV-2 low positives more likely to be cross-reactive false positives.
Western blot (University of Washington)Positive, negative or indeterminate for each typeReference confirmatory test, above 97 percent sensitive and specific. Turnaround 1 to 2 weeks. Used for low-positive or conflicting enzyme immunoassay results.
HSV IgMNot recommendedNot type-specific, positive in recurrences as well as new infection, and prone to false positives. The CDC advises against using it; an isolated positive IgM should not be read as recent infection.
Lesion PCR swabDetected (HSV-1 or HSV-2) or not detectedThe test of choice for an active sore, far more sensitive than culture and gives the type. A positive swab with a negative IgG means a new (primary) infection.

Positive HSV IgG (HSV-1 or HSV-2 antibodies detected)

A positive HSV-2 IgG with an index above 3.0 to 3.5, or a confirmed low positive, means you have HSV-2 infection, almost always genital, acquired at some point in the past. Most people in this position have never noticed an outbreak: around 87 percent of Americans with HSV-2 antibodies have not been diagnosed, and when shown what to look for, many recognize mild recurrent symptoms they had attributed to friction, yeast or ingrown hairs. The infection is lifelong, the virus is shed from genital skin without symptoms on roughly 10 to 20 percent of days, and it can be passed on during those periods, which is the main practical implication of a positive result.

A positive HSV-1 IgG is a different message. About half of adults carry HSV-1, most from a childhood oral infection that may never have produced a visible cold sore, and the blood test cannot tell oral from genital infection. If you have never had genital symptoms, the most likely explanation is oral HSV-1. If you have had genital sores, HSV-1 genital herpes is the likely diagnosis, and it recurs far less often than HSV-2 (typically once a year or less versus four to five times a year in the first year) and is shed less often. Only a swab of a genital lesion can prove the site.

A low-positive HSV-2 result (index 1.10 to 3.0) in someone without symptoms or a known exposure is more likely to be false than true, mainly because antibodies to HSV-1 cross-react weakly with the HSV-2 antigen. Before acting on it, ask for a Western blot or a second assay based on a different method; if confirmation is negative, you do not have HSV-2. A positive IgG does not require treatment by itself. Suppressive antiviral treatment is an option for people with frequent recurrences or who want to lower the risk of passing the virus to a partner, and it is a decision made with your clinician rather than a reflex response to the number.

Common causes

  1. Genital HSV-2 infection, past or present

    The usual meaning of a confirmed HSV-2 positive. About 12 percent of US adults aged 14 to 49 carry HSV-2; the antibody persists for life, so the test cannot say whether infection was last month or 20 years ago.

  2. Oral HSV-1 infection (cold sores), usually acquired in childhood

    The usual meaning of a positive HSV-1 result, present in about half of adults. Many have never had a recognizable cold sore; the virus sits in the trigeminal nerve ganglion and is shed from saliva intermittently.

  3. Genital HSV-1 infection

    Now the cause of about half of first-episode genital herpes in young adults, usually acquired through oral sex from a partner with oral HSV-1. The blood test looks identical to oral HSV-1; only a lesion swab proves the site.

  4. False-positive low-index HSV-2 result

    The main pitfall of the test. Cross-reactive HSV-1 antibody, nonspecific binding and assay variability produce HSV-2 index values of 1.10 to 3.0 in people who do not have HSV-2; about half of such results fail Western blot confirmation in low-risk groups.

  5. Recent infection with antibodies still rising

    In the first weeks after a new infection the index climbs from equivocal to low positive to high positive. A repeat test in 4 to 6 weeks showing a clear rise confirms a new infection; a stable low value favors a false positive.

  6. Maternal antibody in infants

    IgG crosses the placenta, so babies of mothers with HSV antibodies test positive for 6 to 12 months without being infected. Neonatal herpes is diagnosed by PCR of blood, spinal fluid and skin swabs, never by IgG.

  7. Interfering antibodies and laboratory variability

    Autoimmune disease, recent other viral infections and high immunoglobulin levels occasionally produce nonspecific positives on enzyme immunoassays; results near the cutoff also vary from run to run. Confirmation on a different platform resolves most of these.

Symptoms that can go with it

  • None in most people: the majority with HSV-2 antibodies have never had a recognized outbreak, and most with HSV-1 have never had a cold sore
  • First genital episode: clusters of painful blisters that break into shallow ulcers, with fever, swollen groin nodes, painful urination and flu-like aches, lasting 2 to 4 weeks
  • Recurrences: tingling, itching or burning for a day or two (the prodrome), then a small patch of blisters or ulcers that heals in 5 to 10 days, more often with HSV-2 than HSV-1
  • Atypical genital symptoms: recurrent small cracks or fissures, redness, itching or irritation often mistaken for yeast infection, friction, ingrown hairs or urinary infection
  • Cold sores on the lip or around the mouth, often triggered by sun, fever, stress or menstruation (usually HSV-1)
  • Buttock, thigh or low-back pain or tingling before a genital outbreak, from the nerve the virus lives in
  • Rarely: severe headache with stiff neck (HSV-2 meningitis), eye pain and light sensitivity (HSV keratitis), or widespread sores in people with weakened immunity

Negative HSV IgG

A negative HSV-2 IgG (index below 0.90) more than 12 to 16 weeks after your last possible exposure means you have not acquired HSV-2; the assays miss only a few percent of established HSV-2 infections. A negative HSV-1 result is weaker evidence, because the common enzyme immunoassays miss up to 30 percent of true HSV-1 infections, so a negative HSV-1 with a history of cold sores or a positive lesion swab is a false negative rather than a mystery.

A negative result inside the window period is not final. Most people seroconvert by 6 to 12 weeks, but some take 16 weeks or more, and a negative blood test during a first outbreak is expected rather than reassuring (the swab makes the diagnosis). Being HSV-2 negative while a partner is positive is the situation where the test is most useful: it identifies the person at risk, and daily suppressive therapy in the positive partner plus condoms cut transmission substantially.

Common causes

  1. No infection with that type

    The expected result for HSV-2 in about 88 percent of US adults and for HSV-1 in about half.

  2. Testing inside the window period

    Antibody takes 2 to 12 weeks to form, occasionally longer. A first outbreak with a positive swab and a negative IgG is a new infection by definition; the IgG turns positive on retesting.

  3. HSV-1 infection missed by the assay

    Enzyme immunoassays for HSV-1 glycoprotein G have sensitivity as low as 70 percent in some studies. Someone with recurrent cold sores and a negative HSV-1 IgG has HSV-1; Western blot usually confirms it.

  4. Weakened antibody production

    Advanced HIV, chemotherapy, immunosuppressive drugs and immunoglobulin deficiencies can blunt the antibody response, giving a negative or equivocal result despite infection.

  5. Antibody levels drifting below the cutoff

    In a small minority of people, particularly with HSV-1 and with low initial index values, antibody falls below the assay cutoff years after infection (seroreversion). The infection is still present even though the test has turned negative.

Symptoms that can go with it

  • None; a negative result causes no symptoms
  • Genital or oral sores with a negative IgG are tested by PCR swab of the sore, since a new infection has not yet produced antibodies

Read it alongside

  • HSV PCR swab of a sore — the test of choice for any active lesion; it is more sensitive than culture, gives the type, and proves the site in a way the blood test cannot.
  • HSV Western blot — the confirmatory test for low-positive, equivocal or conflicting IgG results, with sensitivity and specificity above 97 percent.
  • A second type-specific assay on a different platform — an acceptable alternative to Western blot for confirming a low-positive HSV-2 result when the reference test is unavailable.
  • HIV antigen/antibody test — HSV-2 roughly triples the risk of acquiring HIV, and HIV changes how herpes behaves, so the two are tested together.
  • Syphilis screen (RPR or treponemal antibody) — a painless genital ulcer is syphilis until proven otherwise, and the two can coexist.
  • Chlamydia and gonorrhea NAAT — recurrent urinary symptoms attributed to herpes may be urethritis from another cause.
  • Cerebrospinal fluid HSV PCR — if severe headache, stiff neck or confusion accompany an outbreak, to diagnose HSV meningitis.
  • Pregnancy test (hCG) — HSV status and timing matter in pregnancy, where a first infection in the third trimester carries the highest risk to the baby.

What usually happens next

  1. A low-positive HSV-2 result (index 1.10 to 3.0) without symptoms: ask for a Western blot or a second assay before telling partners or starting treatment; around half of these results are false.
  2. A high-positive HSV-2 result: the diagnosis is HSV-2 infection, almost certainly genital. The useful next conversation covers recognizing mild recurrences, how asymptomatic shedding works, whether suppressive antiviral therapy fits your situation, and how to tell partners.
  3. A positive HSV-1 result without genital symptoms: most likely oral infection, shared by half the population. No action is needed beyond knowing you can pass HSV-1 on through kissing or oral sex, including when no cold sore is visible.
  4. An equivocal result or a negative result within 12 weeks of an exposure: repeat at 12 to 16 weeks. Any sore in the meantime is swabbed for PCR rather than waiting for the blood test.
  5. If your partner has herpes and you test negative: the practical levers are daily suppressive therapy for the positive partner, condoms, and avoiding sex during prodrome and outbreaks; repeat testing is only needed after a suspected new infection.
  6. If you are pregnant or planning pregnancy with a positive HSV-2 result or a partner who is positive: tell your obstetric team early, since suppressive therapy from 36 weeks and delivery planning reduce the already small risk to the baby.

Diet, lifestyle and natural levers with evidence

What can move HSV IgG once the cause is known. Nothing here replaces finding the cause.

Time the test at 12 to 16 weeks and confirm any low-positive HSV-2 result

Strong evidence

Nothing dietary changes an antibody result; timing and confirmation do. In seroconversion studies the median time to a positive HSV-2 enzyme immunoassay was about 3 to 4 weeks, most people were positive by 12 weeks and a few took longer, so an early negative is repeated. In clinic studies, only about 40 to 50 percent of HSV-2 index values between 1.1 and 3.0 were confirmed by Western blot, compared with more than 90 percent above 3.5; asking for confirmation is the single most useful step after a low positive.

Suppressive antiviral therapy, if you want fewer outbreaks or lower transmission risk

Strong evidence

Not a natural lever, but the only one with large-trial evidence. Daily valacyclovir, acyclovir or famciclovir reduces recurrences by 70 to 80 percent, and in a trial of 1,484 couples daily valacyclovir taken by the partner with HSV-2 cut transmission to the uninfected partner by 48 percent (and symptomatic infection by 75 percent) over 8 months. Condoms add roughly a 30 percent reduction. None of this changes the IgG result, which stays positive for life.

L-lysine

Preliminary evidence

The most studied supplement for recurrences, with mixed results. A 6-month double-blind crossover trial of 1,000 mg three times daily reported fewer and milder recurrences, while other trials at lower doses found no effect; a 2017 review concluded that doses under 1 g a day are ineffective and that 3 g a day may reduce recurrence frequency in some people. There is no evidence it affects antibody levels, shedding or transmission.

High doses can cause stomach upset and have been linked in case reports to kidney problems; avoid at gram doses if you have kidney disease, and tell your clinician if you take it alongside calcium supplements.

Lemon balm cream for cold sores

Preliminary evidence

In a randomized, placebo-controlled trial of 66 people with recurrent cold sores, a 1 percent lemon balm (Melissa officinalis) cream applied four times daily from the first symptoms significantly reduced redness and swelling by day 2 and shortened the episode. The effect is on the sore, not on the virus in the nerve or on antibodies, and it has not been tested for genital herpes.

Sun protection and trigger management

Preliminary evidence

Ultraviolet light is a well-documented trigger for oral recurrences: in a small crossover trial, cold sores developed after experimental UV exposure in 27 of 38 participants using placebo and 1 of 35 using sunscreen on the lips. Fever, menstruation, poor sleep, friction and psychological stress are reported triggers for genital recurrences in cohort studies, though their effects are modest and inconsistent. Managing them may reduce outbreaks; it does not alter the blood test.

When to see a clinician promptly

  • A first outbreak during pregnancy, or a positive HSV-2 result when you are pregnant or planning to be: timing of infection determines the risk to the baby, and suppressive therapy from 36 weeks is routinely offered.
  • A newborn with blisters, fever, poor feeding, lethargy or seizures in the first 4 weeks of life, whether or not the mother has a known herpes diagnosis: neonatal herpes is an emergency treated with intravenous antivirals.
  • A first genital outbreak with inability to pass urine, severe headache with stiff neck, confusion, or eye pain and light sensitivity: urinary retention, HSV meningitis and HSV keratitis need same-day care.
  • Outbreaks that are unusually severe, widespread or slow to heal, especially if you have HIV, are on chemotherapy or take immunosuppressants.
  • A low-positive HSV-2 result (index 1.10 to 3.0) without symptoms: ask for confirmatory testing before accepting the diagnosis or informing partners.
  • Distress, anxiety or relationship difficulty after a positive result: the diagnosis is common, manageable and compatible with normal relationships and childbearing, and counseling is part of good herpes care.

Frequently asked questions

What is a normal HSV IgG index value?

On the most widely used assays, an index below 0.90 is negative, 0.90 to 1.09 is equivocal and 1.10 or higher is positive, for both HSV-1 and HSV-2. The index is your sample's signal divided by a calibrator, not a measure of how much virus you have or how infectious you are, and values are not comparable between different laboratories' assays. Any positive value above about 3.5 for HSV-2 is almost always a true positive; values between 1.10 and 3.0 need confirmation.

What does an HSV-2 IgG of 1.5 or 2.0 mean?

Technically positive, but in the low-positive band where false positives are common. In studies of people without symptoms, only about 40 to 50 percent of HSV-2 index values between 1.1 and 3.0 were confirmed by Western blot, usually because HSV-1 antibodies cross-react. Ask for a Western blot or a second assay on a different platform; if that is negative, you do not have HSV-2. If you have had genital sores or a partner with HSV-2, the same value is more likely to be real.

HSV-1 test results range: what do the numbers mean?

The same cutoffs apply: below 0.90 negative, 0.90 to 1.09 equivocal, 1.10 and above positive. A positive HSV-1 IgG, whether 1.3 or 20, means past infection with HSV-1, which about half of adults have, usually as oral herpes from childhood. A higher number does not mean genital infection, more severe disease or recent infection. Because the assay misses up to 30 percent of HSV-1 infections, a negative HSV-1 result is less certain than a negative HSV-2 result.

How accurate is a herpes blood test?

For HSV-2, type-specific IgG tests are 80 to 98 percent sensitive and about 96 percent specific, which sounds good but means that in people without symptoms, many low-positive results are false; high positives are reliable. For HSV-1, sensitivity is lower (70 to 90 percent), so false negatives are the main problem. The Western blot is over 97 percent accurate for both and is used to confirm uncertain results. For an actual sore, a PCR swab is more accurate than any blood test.

Why is routine herpes blood testing not recommended?

The US Preventive Services Task Force (2023) and the CDC recommend against screening people without symptoms because the test produces many false positives at low index values, a positive result in someone without symptoms does not change treatment or clearly reduce transmission, and the diagnosis causes real distress. Testing is recommended when it changes decisions: recurrent genital symptoms with negative swabs, a partner with genital herpes, people with HIV, or someone requesting a complete STI evaluation after counseling.

How soon after exposure does a herpes blood test turn positive?

IgG antibodies appear a median of 3 to 4 weeks after infection on enzyme immunoassays, most people are positive by 6 to 12 weeks, and a small number take 16 weeks or longer. A conclusive negative therefore requires testing at 12 to 16 weeks after the last possible exposure. If you develop a sore before then, a PCR swab of the sore diagnoses the infection and its type immediately, and a negative IgG at that point simply confirms it is new.

I tested positive for HSV-1. Do I have genital herpes?

Not necessarily, and the blood test cannot tell. About half of adults are HSV-1 positive, mostly from oral infection acquired in childhood, often without ever having a visible cold sore. HSV-1 does cause about half of new genital herpes in young adults, so if you have had genital sores, HSV-1 genital infection is likely; if you have not, oral HSV-1 is the most probable explanation. Only a swab of a genital lesion can establish the site.

Can an HSV IgG test tell how long I have had herpes or who gave it to me?

No. IgG persists for life at levels that do not reflect timing, and the index value does not indicate how long ago infection occurred. The only way to show a new infection is a positive lesion swab with a negative or newly rising IgG, repeated a few weeks apart. Because most people with herpes do not know they have it, and because HSV can be carried silently for decades, a positive result in a long-term relationship is not evidence of recent infidelity by either partner.

References

  1. Herpes (HSV) test. MedlinePlus, US National Library of Medicine (2024)View source
  2. Workowski KA, Bachmann LH, Chan PA, et al.. Sexually transmitted infections treatment guidelines, 2021: genital herpes. MMWR Recommendations and Reports (2021)
  3. US Preventive Services Task Force. Serologic screening for genital herpes infection: US Preventive Services Task Force reaffirmation recommendation statement. JAMA (2023)
  4. McQuillan G, Kruszon-Moran D, Flagg EW, Paulose-Ram R. Prevalence of herpes simplex virus type 1 and type 2 in persons aged 14–49: United States, 2015–2016. NCHS Data Brief, No. 304 (2018)
  5. Morrow RA, Friedrich D, Krantz E. Performance of the Focus and Kalon enzyme-linked immunosorbent assays for antibodies to herpes simplex virus type 2 glycoprotein G in culture-documented cases of genital herpes. Journal of Clinical Microbiology (2003)
  6. Ashley-Morrow R, Krantz E, Wald A. Time course of seroconversion by HerpeSelect ELISA after acquisition of genital herpes simplex virus type 1 (HSV-1) or HSV-2. Sexually Transmitted Diseases (2003)
  7. Agyemang E, Le QA, Warren T, et al.. Performance of commercial enzyme-linked immunoassays for diagnosis of herpes simplex virus-1 and herpes simplex virus-2 infection in a clinical setting. Sexually Transmitted Diseases (2017)
  8. Corey L, Wald A, Patel R, et al.. Once-daily valacyclovir to reduce the risk of transmission of genital herpes. New England Journal of Medicine (2004)
  9. Mailoo VJ, Rampes S. Lysine for herpes simplex prophylaxis: a review of the evidence. Integrative Medicine (Encinitas) (2017)
  10. Koytchev R, Alken RG, Dundarov S. Balm mint extract (Lo-701) for topical treatment of recurring herpes labialis. Phytomedicine (1999)
  11. Rooney JF, Bryson Y, Mannix ML, et al.. Prevention of ultraviolet-light-induced herpes labialis by sunscreen. The Lancet (1991)
  12. Herpes simplex virus (HSV) infections. Merck Manual Professional Version (2024)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.