--is the most sensitive but least specific of the celiac panel tests, but it is often the first test to turn "out of range", and is often the only sign of gluten problems in those who have some degree of sensitivity but may not (yet) have frank celiac.
The problem is that gluten sensitivity has many different presentations--for some people the first signs are not gastrointestinal but neurologic.
What I meant by "don't expect dramatic improvement" is that it takes time for this damage to occur, so it takes time for it to heal, especially if there is villious atrophy causing malabsorption. This is not to say that some people don't feel better fairly quickly, but generally this is a gradual process.
You need to get up to speed on gluten issues quickly--I recommend as a good first stop The Gluten File, put together by the semi-famous jccglutenfree (AKA Cara) and easily linked to right in this forum:
I think this is still the single most comprehensive database on the subject, as it brings in papers and studies across the spectrum of gluten sensitivity. Cara has been maintaining it for years and I give her a great amount of the credit a decade or more back for bringing the whole issue out of the doldrums and into public awareness.