<<Disclaimer: Verify this information before applying it to your situation.>>
 
Hal, a dermatologist diagnosed DH just by looking at my gorgeous
initial set of lesions 18 years ago, but a (later) skin-plug test was
inconclusive.  In spite of no positive test, I've assumed he was
right about DH.  Occasionally my skin would again break out, and
it seemed to me that the most likely culprit had been eaten about
three days earlier.  But this was a bit of a guess since I never
intentionally ingested gluten.
 
Btw, I tried using dapsone shortly after being diagnosed.  I _hated_
the way it made me feel -- spaced out, freaky, outside of my body,
etc -- the way some people apparently take street drugs in order to
feel, brother they can keep it. I couldn't stand it.  Quit at once.
How do y'all who use dapsone react to it, if at all?   After that,
I controlled outbreaks via a prescription cortisone cream, used very
very sparingly.
 
Good luck in your research.