The doctor will infer the diagnosis based on the information provided by the patient and the physical examination. The characteristic appearance of herpes does not question the diagnosis, so the typical appearance of the ulcer is the key to diagnosis. This helps the appearance of the mouth to distinguish between oral herpes thrush, shingles, gonorrhea and syphilis. In addition, chap or sunburned lips may resemble oral herpes, but histological staining (Tzanck smears, see below) does not show virus-induced cell changes. Further testing is usually not necessary, but it is sometimes completed.
If a clear diagnosis is required, for example, because the infection involves other organ systems, the doctor can perform the following laboratory tests:
Sample (tissue or fluid) from ulcer identifies virus as HSV
Virus culture analysis
Stain test called Tzanck smear (showing nonspecific nuclear changes caused by HSV)
Antigen and antibody studies (serological and PCR tests to determine if the infection was caused by HSV-1 or HSV-2)
