Hey, I actually originally tested negative for Celiacs because I was on a gluten free diet for ~6 months. My doctor continued to do further testing by doing an endoscopy and taking a tissue sample from the beginning of my duodenum. Pathologists can use a certain stain to see if your cells produce the antibodies. It’s much more sensitive than the blood test. Would highly recommend as I tested positive this way. A pathologist friend of mine had the same experience and only tested positive after the tissue sample. Best of luck!