Herpes Tests

Test Overview

Herpes tests are done to find the herpes simplex virus (HSV). An HSV infection can cause small, painful sores that look like blisters on the skin or the tissue lining (mucous membranes) of the throat, nose, mouth, urethra, rectum, and vagina. A herpes infection may cause only a single outbreak of sores, but in many cases the person will have more outbreaks.

There are two types of HSV.

  • HSV type 1 causes cold sores (also called fever blisters) on the lips. HSV-1 is generally spread by kissing or by sharing eating utensils (such as spoons or forks) when sores are present. HSV-1 can also cause sores around the genitals.
  • HSV type 2 causes sores in the genital area (genital herpes), such as on or around the vagina or penis. HSV-2 also causes the herpes infection seen in babies who are delivered vaginally in women who have genital herpes. HSV-2 is generally spread by sexual contact. HSV-2 can sometimes cause mouth sores.

In rare cases, HSV can infect other parts of the body, such as the eyes and the brain.

Tests for HSV are most often done only for sores in the genital area. The test may also be done using other types of samples, such as spinal fluid, blood, urine, or tears. To see whether sores are caused by HSV, different types of tests may be done.

  • Herpes viral culture. Cells or fluid from a fresh sore are collected with a cotton swab and placed in a culture cup. The culture often fails to find the virus even when it is present (false-negative results).
  • Herpes virus antigen detection test. Cells from a fresh sore are scraped off and then smeared onto a microscope slide. This test finds markers (called antigens) on the surface of cells infected with the herpes virus. This test may be done with or in place of a viral culture.
  • Polymerase chain reaction (PCR) test. A PCR test can be done on cells or fluid from a sore or on blood or on other fluid, such as spinal fluid. PCR finds the genetic material (DNA) of the HSV virus. This test can tell the difference between HSV-1 and HSV-2. Using the PCR test on skin sores isn't common. PCR is used mainly for testing spinal fluid in rare cases when herpes may have caused an infection in or around the brain.
  • Antibody tests. Blood tests can find antibodies that are made by the immune system to fight a herpes infection. Antibody tests are sometimes done but are not as accurate as a viral culture at finding the cause of a specific sore or ulcer. Antibody tests cannot always tell the difference between a current active herpes infection and a herpes infection that occurred in the past. Because antibodies take time to develop after the first infection, you may not have a positive antibody test if you have just recently been infected. Some blood tests can tell the difference between HSV-1 and HSV-2.

About 1 out of 6 adults in the United States have antibodies to HSV-2, the virus typically linked to genital herpes.1

A herpes infection cannot be cured. After you become infected with HSV, the virus stays in the body for life. It "hides" in a certain type of nerve cell and causes more outbreaks of sores in some people. Recurring infections can be triggered by stress, fatigue, sunlight, or another infection, such as a cold or flu. Medicine can relieve symptoms and shorten the length of the outbreaks, but medicine cannot cure the infection.

A different herpes virus (called varicella zoster) causes chickenpox and shingles.

Why It Is Done

A test for herpes may be done to:

  • Find out whether HSV is causing sores around the mouth or in the genital area.
  • Find out which virus type (HSV-1 or HSV-2) is causing sores around the mouth or in the genital area.
  • Find out whether the sex partner of a person with genital herpes may be infected with HSV.
  • Diagnose a herpes infection in a newborn baby whose mother has genital herpes.

How To Prepare

If you may have genital herpes, do not have sexual contact until your test results are back. You can lower the chance of spreading the disease to your partner(s).

How It Is Done

For a viral culture, viral antigen test, or PCR test, a clean cotton swab is rubbed against a herpes sore to collect fluid and cells for examination. Samples may be collected from the vagina, cervix, penis, urethra, eye, throat, or skin. Doctors usually collect a sample from small sores that are only a few days old. Viruses are more likely to be found in small newly formed sores.

For an antibody test, the health professional drawing blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

How It Feels

You are likely to feel some mild discomfort or pain when the sores are scraped to collect a sample for testing.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

If an antibody test is done, there is very little chance of problems from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

Herpes tests are done to find the herpes simplex virus (HSV). Results for a rapid viral culture may take 2 to 3 days, while results for a standard culture can take up to 14 days. Antigen detection test results are ready in a day. Polymerase chain reaction (PCR) test results are ready in 1 to 3 days. Results from an antibody blood test are ready in 2 days. The results from an antibody test called an enzyme-linked immunosorbent assay (ELISA, EIA) may be ready in about 2 hours.

Herpes tests
Normal:

Normal results are called negative.

No HSV grows in the viral culture.

No viral antigens or DNA are found.

No herpes antibodies are present in the blood.

Abnormal:

Abnormal results that show HSV are called positive.

HSV grows in the viral culture.

HSV antigens or DNA are found.

Antibodies to the herpes virus are present in the blood.

Samples taken from newly formed sores containing fluid (blisters) are generally better than samples collected from older, crusted sores.

A normal (negative) test result does not mean you do not have a herpes infection. If the first test is negative but you have symptoms of herpes, more tests may be done.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • If a culture sample is taken from a crusted, older sore.
  • If a blood sample is taken before antibodies against HSV have formed. This period is called the window period or seroconversion period.
  • If you are taking antiviral medicines, such as acyclovir, famciclovir, ganciclovir, or valacyclovir.

What To Think About

  • Normal test results do not mean you do not have a herpes infection.
  • Herpes is often diagnosed by symptoms and by knowing whether the person has had contact with an infected person. Sometimes a test is not needed. A person who has genital herpes needs to learn how to avoid spreading the disease, because the disease is more likely to be spread when he or she has sores. If you have recurrent outbreaks, especially during times of stress or illness, you can also spread the disease.
  • You may want to know whether a herpes infection is due to HSV-1 or HSV-2 so you can take steps to prevent or treat outbreaks.
  • A genital herpes infection can be spread from a mother to her baby during vaginal delivery. In a newborn, herpes can cause organ failure, brain infection, and death. If active herpes is present near the time of delivery, a cesarean delivery (C-section) may be done to prevent infecting the baby.
  • Rapid tests are available at some clinics that check blood from a finger stick for antibodies to HSV-2. The results are generally ready in about 10 minutes. These tests are more expensive than other tests and may not be available everywhere.

References

Citations

  1. Centers for Disease Control and Prevention (2010). Seroprevalence of herpes simplex virus type 2 among persons aged 14–49 years—United States, 2005–2008. MMWR, 59(15): 456–459. Also available online: http://www.cdc.gov/mmwr/pdf/wk/mm5915.pdf.

Other Works Consulted

  • American College of Obstetricians and Gynecologists (2007, reaffirmed 2009). Management of herpes in pregnancy. ACOG Practice Bulletin No. 82. Obstetrics and Gynecology, 109(6): 1489–1498.
  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.

Credits

By Healthwise Staff
Sarah Marshall, MD - Family Medicine
Jeanne Marrazzo, MD, MPH - Infectious Disease
Last Revised December 20, 2012

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

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