Doctors most often use blood tests and biopsies of the small intestine to diagnose or rule out celiac disease. Doctors don't recommend starting a gluten-free diet before diagnostic testing because a gluten-free diet can affect test results.
Two blood tests can help diagnose it: Serology testing looks for antibodies in your blood. Elevated levels of certain antibody proteins indicate an immune reaction to gluten. Genetic testing for human leukocyte antigens (HLA-DQ2 and HLA-DQ8) can be used to rule out celiac disease