There is no diagnostic test that a Dermatologist can do. A biopsy does not confirm the diagnosis and is usually not recommended. A dermatologist will look at the area and might say that what you have is consistent with bed bug bites and may prescribe treatment to help with the itch. Most of the work is on you--to see if you have them at home and to get rid of them. Look at the list of things to look for on this page.