The most accurate way to diagnose herpes via testing depends on whether you have an active outbreak or not. If you have herpes blisters, a swab test viral culture can be done to determine if either HSV-1 or HSV-2 is causing cold sores or genital sores. If there is no active outbreak with symptoms, blood tests are the only way to determine if you have previously been exposed to either type of herpes simplex virus, although blood tests may not be able to tell you if you are actively contagious. Once your body has been exposed to HSV, your body makes antibodies. These can persist for years, so a blood test may not be able to tell you if you got infected recently or many years before.