What Is a Herpes IgG Test?

Blood test used to detect genital herpes antibodies

Doctor drawing blood for medical testing

Astrakan Images / Getty Images

Herpes IgG test is a type of blood test used to detect herpes simplex virus (HSV). It does not identify the actual virus but rather the immune proteins (called antibodies) that your body produces in response to the infection.

Immunoglobulin G (IgG) is one type of antibody that is "tailor-made" to attack a specific disease-causing agent (called a pathogen). Herpes IgG is the type produced when an HSV infection occurs.

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

Purpose of Test

A herpes IgG test is typically used to confirm a genital herpes infection. It can be performed alongside a herpes viral culture (in which fluid from an open sore is cultured in the lab) or an HSV polymerase chain reaction (in which HSV DNA is detected from cells of fluids in a genital sore).

The herpes IgG test aims to identify whether you have been exposed to the HSV-1 (the type primarily associated with cold sores) or HSV-2 (the type that mainly causes genital herpes). 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.

The herpes IgG test does have its limitations. Because the test identifies the body's response to HSV, rather than to the virus itself, it can take up to four months before enough IgG is produced to render an accurate diagnosis.

On the flip side, one of the advantages of the IgG test it is better able to differentiate HSV-1 from HSV-2 compared to the IgM test.

Herpes IgG testing
Verywell / Cindy Chung

Risks and Contraindications

There are no contraindications for herpes IgG testing, and the risks associated with the procedure are very low. However, there are limitations as to when the test should be used. This is due in part to the fact that herpes, while distressing, is usually not serious outside of pregnancy.

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

Before the Test

The herpes IgG test requires no preparation other than your readiness to take the test. While it is not used for the routine screening of people without symptoms, it should be used in pregnant women whose partner has genital herpes to avoid neonatal herpes.

Timing

The herpes IgG test takes only a few minutes but should not be performed in the window period (the time between exposure and the production of detectable antibodies). The minimum window period for HSV is four to six weeks after the suspected exposure. Anything earlier would likely return a false-negative result.

By contrast, the herpes IgM antibodies reach detectable levels within seven to 10 days of exposure and start to decline after two weeks. As such, the herpes IgM test is ideal during acute infections, while herpes IgG can detect infection years after the exposure.

Location

Herpes blood tests can be conducted at 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 for a herpes IgG or IgM blood test.

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.

Cost and Insurance

Depending on where you live and the lab you use, a herpes IgG test can cost anywhere from $20 to $65. Public clinics tend to be the least costly.

Even though genital herpes is considered a sexually transmitted disease (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.

During the Test

Upon arrival at the testing site, you will be asked to register and confirm your insurance information, if needed. You will likely be asked to complete a health questionnaire and sign a consent form.

Because genital herpes is not a notifiable disease like HIV or hepatitis, your information 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 but are advised for all people in high-risk groups. This includes chlamydia and gonorrhea testing in sexually active women or HIV testing in all people ages 15 to 65.

Throughout the Test

A herpes blood test is a simple blood draw involving the following steps:

  1. An elastic band is placed around your upper arm to make a 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).

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

After the Test

The blood draw may cause soreness, swelling, and bruising at the injection site. Lightheadedness and infection are also possible.

Interpreting Results

The results of a herpes blood test will generally be reported as positive, negative, or equivocal. A positive result means that IgG was detected, while a negative result means than no IgG was detected. An equivocal test simply means that the results were unclear.

A false-negative result can sometimes occur, most often because testing was performed within the window period. You may also have a false-positive result, usually because the herpes IgM test cannot distinguish between HSV-1 or HSV-2.

It can be difficult to decipher IgG and IgM results when performed together. It's important to remember that 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.

Therefore, if you test positive for IgG but not IgM, you have probably been infected for at least two months. People with newer infections are more likely to test positive for IgG and IgM or just IgM alone.

The converse is not true. Having positive IgG and IgM results doesn't necessarily mean that you were infected recently. In fact, 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. 

  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 herpes symptoms, go to your doctor right away. Sores can be tested directly without the need for a waiting period. This is invariably faster waiting for antibodies and far more accurate.

However distressing the condition may be, it is important to remember that you can live a long and happy life with herpes. If you test positive for herpes, get the support and counseling needed to overcome any fears or concerns you may have.

A herpes diagnosis can seem overwhelming, but you are not alone. According to the CDC, no less than one in eight American ages 14 to 49 are affected by HSV-2.

Even if symptoms are severe, you can take comfort in the fact the will usually get better with time. In some cases, there may not be any recurrence of symptoms after the initial outbreak.

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Article Sources

  1. 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.

  2. Centers for Disease Control and Prevention. Genital Herpes Screening FAQ. Atlanta, Georgia; February 9, 2017

  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. 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.

  6. 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.

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