Any doc worth his/her salt will DX someone based on several signs symptoms and test results and not exclude a DX because of one unexpected test result. So, if he's having Celiac symptoms and a positive TTG that should be enough to know it's Celiac.
I will warn that when dealing with kids, even the top Celiac Dr's see this differently. I don't see the childs age posted but if they are younger then it's seen as a different ballgame in some regards.
You may be able to have Chicago look at your slides. You would need to call them. They (most likely) will not consult over the phone. There are legal issues with insurance billing and having to actually see the patient. Though once you see them you should be able to do other stuff over the phone.