A doctor diagnoses gluten intolerance, also called Celiac Disease, by taking blood tests for certain antibodies. If the blood tests are positive, the doctor performs a biopsy of the small intestine to check for damage. Once the diagnosis is confirmed, the treatment is a gluten-free diet. In gluten intolerance, ingesting these foods causes an immune reaction, which damages the small intestine. Gluten is a protein in wheat, rye and barley. A trial of a gluten-free diet can confirm the diagnosis. Try not to start the diet before the medical evaluation because you might change the test results and complicate the diagnosis.