Non-celiac gluten sensitivity is differentiated from celiac disease because the latter is specific to genetics that causes many or most with this genetic code to experience a range of serious symptoms when exposed to gluten. More specifically, GCGS is defined as as sensitivity to gluten when celiac disease and wheat allergy have been ruled out.
Celiac disease is complex and hard to catch, see celiac disease symptoms. Once suspected however, clinical tests are greatly improved over what used to be available. In the absence of a definitive celiac or wheat allergy result, you can go with gluten allergy or NCGS because treatment is the same: avoid all gluten. 
NCGS is considered a non-immune response by some  so you could exclude gluten allergy in the definition of NCGS, but such nitpicking is not necessarily helpful to you if you are simply following a gluten free diet because you notice symptoms you can’t live with when you get gluten which go away after some time when you stop eating it. The same could be said for celiac disease, although there are differences.
NCGS vs. Celiac Disease Differences
As mentioned earlier, celiac disease has a specific set of symptoms, but they are wide ranging and variable so perhaps specific is not quite the right word. To give you an example, thyroid problems, diabetes and bowl cancer can all be symptoms of celiac disease. The same cannot be said for NCGS, on the other hand future studies may prove otherwise.
Non-Celiac Gluten Sensitivity Definition
According to Mansueto P, NCGS can be described as follows:
“A significant percentage of the general population report problems caused by wheat and/or gluten ingestion, even though they do not have celiac disease (CD) or wheat allergy (WA), because they test negative both for CD-specific serology and histopathology and for immunoglobulin E (IgE)-mediated assays. Most patients report both gastrointestinal and nongastrointestinal symptoms, and all report improvement of symptoms on a gluten-free diet. This clinical condition has been named non-celiac gluten sensitivity (NCGS).”
What is your experience with Non-Celiac Gluten Sensitivity? Have you been confused between this, celiac disease and gluten allergy on your quest for better health? What tests have you had? Please leave a comment.
 Non-celiac gluten sensitivity: Time for sifting the grain: “Subjects with NCGS claim a variety of intestinal and/or extra-intestinal symptoms, similar to those occurring in patients affected by CD or IBS. Symptoms occur after gluten ingestion; they improve/disappear when gluten is withdrawn from the diet or recur within a few hours or days on gluten challenge.”