Genital Herpes Health Center

Tests to Diagnose Genital Herpes

Accurate testing is important for genital herpes. Being told you're infected when you're not, or the other way around, can be awful. Some people have lived decades under the false impression that they were infected because a doctor didn't test them for the virus. Instead, they were diagnosed by their symptoms alone. It's easy to mistake genital herpes symptoms for something else.

If you have sores on your genitals, a doctor can take a sample from a sore and look for the herpes simplex virus (HSV) in it. One test is called a cell culture. Any viruses in the sample are allowed to multiply so that they're easy to find under a microscope. There are other tests, such as PCR, available as well.

The direct fluorescent antibody test is another kind. A solution containing HSV antibodies and a fluorescent dye is added to the sample. Antibodies are proteins produced by the immune system in response to an infection. If the virus is present in the sample, the antibodies stick to it and glow when viewed under a special microscope. 

Unfortunately, an antibody test (usually done on blood samples) only tests whether you have been exposed or ever had herpes virus. It is helpful, but does not diagnose a specific outbreak.

Antibody tests can tell the difference between the two types of HSV. It's important to know which type you have. If you're infected with type 2 (HSV-2), you may have outbreaks more often than would if you had type 1 (HSV-1). What's more, knowing which type you have gives a clue as to how you were infected. HSV-1 usually infects the genitals through oral sex, and HSV-2 usually is passed on during vaginal or anal sex. For help with these terms, see the Glossary.

Cell culture or PCR tests taken from active sores may give a false-negative result if the sores have begun healing. A positive result from one of these tests is very accurate, however.

Blood Tests for Genital Herpes

A blood test can detect HSV antibodies even when you have no symptoms of genital herpes. A false-negative result from a blood test is possible if you have been infected recently. It takes several weeks for HSV antibodies to show up in the blood.

False-positive test results are possible, too. If you test positive, but your risk for getting the virus is low, you may need to be tested again.

These tests are of limited use because they only show that you have been exposed to the virus at some point.  It is difficult to tell from these tests when the exposure may have occurred.  You may have had HSV for many years before you have your first noticeable outbreak.