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. In rare cases, the test may 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. A viral culture is the most specific method of finding a genital herpes infection.
• 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. The PCR test is not often done on skin sores, but it is best for testing spinal fluid, for those rare cases in which herpes may cause 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 occasionally done but are not as accurate as a viral culture at finding the cause of a specific sore or ulcer. Antibody tests cannot 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.