In all reality . . . I'm not sure it matters to have a definite diagnosis of DH. It is just marked on your medical charts and who is that helping? I guess it does matter to be sure it isn't another skin disease.
I think the doctor and/or test being positive about DH is for peace of mind. It sure doesn't help the itch, sting or burn. I have been to 5 dermatologist with 6 biopsies before the head of the university of dermatology took 2 biopsies correctly. Has to be next to a lesion with direct immunofluorescence to see IgA . I had been gluten-free and on Dapsone for 5 months but he still took the biopsies. He didn't think they would show DH but still took them. Now my record with my PCP and this Dermatologist has charted Celiac DH.
I still have the rash, burning, stinging and itch. The healed lesions do turn a purple color and fade to white. They also leave white circles like the pigmentation is gone. I told this last Dermatologist, "It doesn't matter if the biopsy is positive, I know how the gluten-free diet and Dapsone has helped. I came to you because my PCP wanted to be sure it wasn't T-cell Lymphoma as I am a NH Lymphoma (remission) patient." BTW, only 1% of people with Celiac/DH develop NH Lymphoma, a serious complication of gluten enteropathy. I've been sick a long time when a simple change of diet would have healed me.
You could ask for the biopsy to be done correctly but I'm pretty sure the steroids can affect the results. I know I was told by one of the Derms that the topical steroids affected results. If they can't get it right, go gluten free. If you see positive results. . . that is all that matters, at least to me. Good luck!