How is genital herpes diagnosed?

Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

In most cases, doctors can diagnose genital herpes just by looking at the infection. However, your doctor may want to take a small sample of the infection to test for the herpes simplex virus. A blood test can also detect the presence of the herpes simplex virus in your body and determine if it is type 1 or type 2.

Although genital herpes sores may be visible to the naked eye, laboratory tests may be needed to distinguish herpes sores from other infections. For several years, the most common method of diagnosis has been the viral culture. A new sore is swabbed or scraped, and the sample is added to a laboratory culture containing healthy cells.

When examined under a microscope after several days, the cells show changes that indicate growth of the herpes virus. A major disadvantage of viral culture is that the specimen must be collected from a lesion or sore; when the lesion begins to heal, the test becomes unreliable. A test called the polymerase chain reaction (PCR) test is more sensitive than standard culture tests at identifying the herpes virus in the urinary and genital tracts; however, it is expensive and therefore not used very often.

Blood tests have become more popular because they can detect evidence of infection even when sores are not present. These tests can be done on a small amount of blood taken from the arm or finger and, in some settings, results may be available immediately. Because they detect antibody (made by the body in response to the infection) they may not be positive until several weeks after exposure. Because most herpes simplex virus 2 (HSV-2) is genital, a positive blood test for HSV-2 usually indicates genital herpes. Because so many people in the United States have cold sores due to herpes simplex virus 1 (HSV-1), it is not routinely done. However, because genital herpes may be caused by HSV-1, a negative test for HSV-2 does not rule out genital herpes infection due to HSV-1.

Interpretation of test results should be done by a clinician. A major advantage of the HSV-2-specific test is that it can be done when no sore is present. It may, therefore, detect infection in people who have not had recognized symptoms.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.