A blood screening test can be done for Celiac, wheat allergy or gluten sensitivity (non-celiac):
Wheat allergy: Anti-Wheat IgE and IgG (be sure they look at both...IgE is immediate hyersensitivity, IgG is delayed hypersensitivity), and/or skin scratch test for wheat.
Gluten sensitivity: Anti-Gliadin IgG.
Celiac: Anti-Gliadin IgA, Anti-Gliadin IgG, total IgA, Anti-Tissue Transglutaminase antibodies, and sometimes Endomysium antibodies.
Special stool studies and/or genetic tests can also help confirm a diagnosis of Gluten Sensitivity - see http://www.enterolab.com/
Also, for the "Gold Standard" Celiac diagnosis, one must show villous atrophy on biopsy of the small intestine (this requires an endoscopy procedure done by a Gastroenterologist).
Dietary gluten avoidance (minimum 3-6 months - because it can take that long for the gut to heal after gluten has been removed from one's diet), followed by a gluten challenge (eat 1 thing containing gluten, such as a cookie or piece of bread), can sometimes reveal a gluten problem that is unable to be detected via blood test, stool test, or small bowel biopsy. This method can also be used to confirm a diagnosis if tests are inconclusive.
The best info I know of on all this stuff can be found at The Gluten File - see http://sites.google.com/site/jccglutenfree/
Also, it is known that Lyme disease can trigger a form of gluten sensitivity that may or may not go away with treatment. And some doctors theorize that Celiac disease can be triggered by an infectious agent...
I hope this helps...take care,