J.G.
I would also say allergy test. Keep in mind, for a gluten sensitivity to show they must be on a gluten diet. If you remove gluten from the diet it will not show up in the blood test. You can also test for a genetic marker though. I really like this book..The Gluten Connection by Shari Lieberman. She explains in detail the problem with gluten what could also be the problem, the history of it and why there is more of a problem now than say 20 years ago. She also has a section of if after going gluten free the symptoms come back.
When my son was diagnosed gluten intolerant, I put us all on a gluten free diet. I am pretty positive both my daughter and I have a problem with gluten but since going gluten free, the ped's have said I would not be able to test for it unless I was to go back to gluten for a while. As others have said though, it is very common to get gluten in things you didn't expect. You could have an endoscopy done by a ped. G.I specialist. It is super quick and then you can have some answers.