Herpes tests are done to find out if you have been exposed to 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.
The United States Centers for Disease Control and Prevention (CDC) does not recommend getting a herpes blood test as part of a regular screening for sexually transmitted infections (STIs). That's because a positive result only means you have been exposed to the virus. The test can't tell if you will get sores or if any sores you have are caused by the herpes virus. The test also can't tell if you can infect another person.
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. This is a test to find the herpes virus. Fluid from a fresh sore is added to certain cells used to grow HSV. If no virus infects the cells, the culture is negative. If the herpes virus infects the cells, the culture is positive. The culture often fails to find the virus even when it is present (false-negative results).
- 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.
- 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 can't 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.
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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 or PCR test, a clean cotton swab is rubbed against a herpes sore to collect fluid and cells to examine. 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.
A health professional uses a needle to take a blood sample, usually from an arm.
Rapid tests are available at some clinics. These tests check blood from a finger stick for antibodies to HSV-2. The results are generally ready in about 10 minutes. These tests may not be available everywhere.
How It Feels
You are likely to feel some mild discomfort or pain when the sores are rubbed to collect a sample for testing.
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Test results are ready at different times for the different tests. Some test results may be back the same day. Others may take a few days.
Normal results are called negative.
No HSV grows in the viral culture.
No HSV DNA is found.
No herpes antibodies are present in the blood.
Abnormal results that show HSV are called positive.
HSV grows in the viral culture.
HSV DNA is 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.