Chrons are diagnosed by colon biopsy,colonscopy and blood test for specific antibdoies. Chrons can affect any portions of the intestines, besides the colon, but colon is preferred.
Celiacs is the autoimmune reaction to gluten, "prolamin" proteins of gluten, celiacs is slightly more complicated as well. The stools of celiacs are yellowish, which are sticky foul smelling, and fatty(thats a severe form celiacs). In order to be tested for gluten you should be eating foods containing gluten for several weeks to several months to insure that antibodies will show up. Otherwise your celiacs test will be negative. tHEY WILL DO a small intestinal biopsy to see any villous atrophy(indicative of celiacs). If you are caucasian ancestry, you should get tested for celiacs genes. 1 gene makes you a high risk for celiac, another for gluten insensitivity(not celiacs), wheat allergies is a real allergy so that is different.
Furthermore, if you have blisters, dermatitis herpetiformis(which is a celiacs or gluten sensitivity rash), thats a high indication for one of the diseases, stil you need a skin biopsy to rule it out. You cant be tested for celiacs unless you are consistently eating gluten products for a about a month.
celiacs also have other symptoms, such as association with diabetes type 1, hashimotos,,etc.
if you are gluten free, currently your celiacs test will also be negative. as willl a small intesitnal biopsy.