What Is a Herpes IgG Test?

Blood test used to detect genital herpes antibodies

An immunoglobulin G (IgG) blood test is used in the diagnosis of herpes simplex virus (HSV) infection. This test does not detect the virus—it detects the antibodies (immune proteins) that your body produces in response to the viral infection.

Parts of the IgG protein, like all antibodies, are "tailor-made" by the immune system to attack specific pathogens (disease-causing organisms, like viruses and bacteria). HSV IgG is the type of IgG antibody that's produced when an HSV infection occurs.

The IgG test is not the only antibody test used to detect HSV. There's also an HSV immunoglobulin M (IgM) test that detects IgM. Unlike IgG antibodies that stay in the body for a lifetime, IgM antibodies are short-lasting and can usually only be detected during an active or recent infection.

Purpose of Test

An HSV IgG test is typically used to confirm a genital herpes infection. It is not recommended as a general screening test. It is recommended for pregnant women who are at risk of having genital herpes. Treatment can reduce the risk of transmission to the baby.

It can be performed alongside:

  • A viral culture, in which the actual pathogen is grown in a lab
  • HSV polymerase chain reaction (PCR), which can detect HSV DNA

Both of these tests are done by using fluid that's sampled from an open sore.

The Centers for Disease Control and Prevention (CDC) currently advises against HSV testing for people without symptoms. Doing so has not been shown to alter sexual behaviors or reduce the rate of transmission.

It can take three to six weeks from the initial infection before enough IgG is produced to be detected.

One of the advantages of the IgG test is that it's better able to differentiate HSV-1 (the type primarily associated with cold sores) from HSV-2 (the type that mainly causes genital herpes) compared to the IgM test. With that being said, HSV-1 can cause a genital infection and HSV-2 can cause oral infection, usually as a result of oral sex.

Herpes IgG testing
Verywell / Cindy Chung

Risks and Contraindications

There are no contraindications for HSV IgG testing, and the risks associated with the procedure are very low.

Before the Test

This test requires no preparation, and it only takes a few minutes.

Timing

The minimum window period (the time between exposure and the production of detectable antibodies) for HSV is four to six weeks after the suspected exposure. Anything earlier would likely return a negative result unless you have been infected before.

Having an HSV IgG test early during your infection may be helpful in determining whether you have been exposed to HSV type 1 or type 2 before. If you have clinical signs of an infection and your HSV IgG test is negative, it is likely that you have a new infection and you were never exposed to the virus before. However, you should repeat the test in about four to six weeks to confirm and to determine which type of HSV virus you may have acquired.

By contrast, the HSV IgM antibodies reach detectable levels within seven to 10 days of exposure and start to decline after two weeks. As such, the HSV IgM test can be helpful in the diagnosis during acute infections.

Location

HSV antibody blood tests can be conducted at sexually transmitted disease (STD) clinics, women's health clinics, pathology labs, retail blood testing centers, public clinics, and some HIV service organizations. While some of these centers offer drop-in testing, others may require an appointment and/or a referral. Call in advance for details.

Food and Drink

There are no food or drink restrictions you need to follow before having an HSV IgG or IgM blood test.

Cost and Health Insurance

Depending on where you live and the lab you use, your HSV IgG blood test can cost between $35 to $80. Public clinics tend to be the least costly.

Even though genital HSV is considered an STD, don't assume that a free STD clinic will have the test or provide it free of charge. Some may only offer free testing for HIV, hepatitis, and select STD screening tests.

To ensure the test is available, call the clinic in advance of your arrival. To search for free or low-cost STD clinics in your area, use the GetTested locator offered by the CDC.

What to Bring

If using a public clinic, the facility may require government-issued ID to confirm your residency. Call in advance for details. You should also check to see if they accept your insurance. If so, bring your insurance card and a method of payment if there a copay or coinsurance.

During the Test

Upon arrival at the testing site, you will be asked to register, sign a consent form, and possibly to confirm your insurance information.

Because genital HSV is not a notifiable disease like HIV or hepatitis, your information and results will not be shared with local, municipal, state, or federal health authorities.

Pre-Test

Some STD clinics will conduct a short pre-test counseling. The aim of the counseling is to establish why you feel you need the test and whether you may be at risk of other STDs.

Based on your response, the counselor may recommend additional STD screening. The recommendations may not have anything to do with you personally and are based on guidelines for all people in high-risk groups. This includes chlamydia and gonorrhea testing for sexually active women under age 25, women ages 25 and older, and men if they have certain risk factors or HIV testing in all people ages 13 to 64.

Throughout the Test

An HSV blood test is a simple blood draw involving the following steps:

  1. An elastic band is placed around your upper arm to make a selected vein swell
  2. The injection site is cleaned with an antiseptic swab
  3. A needle is inserted into the vein
  4. Between 8 to 10 milliliters (mL) of blood is extracted into a vacuum-sealed test tube
  5. The needle is removed and your arm bandaged
  6. The tube is sent to a lab for evaluation using an enzyme-linked immunosorbent assay (ELISA)

After the Test

You will have a small puncture wound at the injection site. This should stop bleeding within a few minutes and you should leave the bandage on for about one day to prevent infection.

While it isn't common, you might have soreness, swelling, and/or bruising at the injection site. Lightheadedness and infection are rare, but also possible.

Interpreting Results

Your test results should be ready within two to five working days, but the timing may vary depending on the clinic or lab.

The results of your HSV blood test will generally be reported as positive, negative, or equivocal. A positive result means that IgG was detected, while a negative result means that IgG was not detected.

An equivocal test means that the results were unclear. If your test is equivocal, your doctor might consider your other tests (like culture or PCR) to make your diagnosis or might recommend that you repeat the antibody test after a few weeks.

A diagnosis of HSV can seem overwhelming, but you are not alone. According to the CDC, more than one out of every six people ages 14-49 years have genital HSV.

IgG antibodies take longer to produce, but last a lifetime, while IgM antibodies are detectable after a few days, but dissipate within a few weeks.

  • If you test positive for IgG but not IgM, you have probably been infected for at least two months.
  • If you test positive for IgG and IgM or just IgM alone, then it's likely that you have a new infection.

Having positive IgG and IgM results doesn't necessarily mean that you were infected recently, however. Between 30 and 70 percent of people with recurrent infections will test positive for IgM, according to a 2014 review published in the Virology Journal. 

A false-negative result can sometimes occur, especially if you have your test within the window period. You may also have a false-positive result. And the HSV IgM test cannot distinguish between HSV-1 or HSV-2.

  Positive IgG Negative IgG
Positive IgM Infection date indeterminate Acute/Recent infection
Negative IgM Established Infection No infection detected

A Word From Verywell

If you have symptoms of HSV, it's important that you get medical attention. Your doctor can examine you and order the appropriate tests.

It is important to remember that you can live a long and happy life with herpes. If you test positive for HSV, you should seek treatment and guidance for safe sex.

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Genital Herpes Screening FAQ. Atlanta, Georgia; February 9, 2017

  2. Legoff J, Péré H, Bélec L. Diagnosis of genital herpes simplex virus infection in the clinical laboratory. Virol J. 2014;11:83. doi:10.1186/1743-422X-11-83.

  3. U.S. Preventive Services Task Force (USPSTF). Chlamydia and Gonorrhea: Screening. Rockville, Maryland; September 2014.

  4. U.S. Preventive Services Task Force (USPSTF). Final Recommendation Statement: Human Immunodeficiency Virus (HIV) Infection: Screening. Rockville, Maryland: June 2019.

  5. McQuillan Q, Kruszon-Moran D, Flagg E, and Paulrose-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. Hyattsville, MD: National Center for Health Statistics; 2018.

  6. Legoff J, Péré H, Bélec L. Diagnosis of genital herpes simplex virus infection in the clinical laboratory. Virol J. 2014;11:83. doi:10.1186/1743-422X-11-83.

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