Making the Diagnosis
Gingivitis is easily diagnosed by the appearance of the gums. The appearance of the inflammation will help your doctor or dentist distinguish a bacterial infection from the herpes virus. Scrapings could yield information on the species of bacteria involved, but it's rarely relevant to treatment so it's not generally done.
Occasionally gingivitis is the first sign of some other disease, such as diabetes or leukemia. A doctor may want to give someone with gingivitis a more thorough examination if there is severe gum disease for no apparent reason.