The immunodot assay also looks for antibodies to a specific protein on the herpes virus. It has a sensitivity similar to that of the Western blot assay, and it will also correctly distinguish between HSV-1 and HSV-2. Like the Western blot assay, it is not 100 percent accurate, and it may take time—three weeks to six months after first infection—to show a positive result. Like the Western blot, this assay is useful for retesting a person whose culture was negative but whose symptoms strongly suggest herpes. If such a person notices another genital sore, he or she can either return to the health care provider as soon as possible for another culture or return in three to six months to have the blood test performed.
When genital sores or ulcers are present, other possible diagnoses must be considered. Syphilis, lymphogranuloma venereum, and chancroid are additional sexually transmitted diseases that can cause genital ulcers. In addition, certain medical conditions, such as the inflammatory bowel disorder called Crohn’s disease, can causegenital sores. The autoimmune disease Behcet’s syndrome can cause genital ulcers as well as oral ulcers and conjunctivitis.