<<Disclaimer: Verify this information before applying it to your situation.>> There are basically three serum antibody tests that help towards the diagnosis of celiac disease. The specificity and sensitivity of these tests varies depending upon the test method and the skills of the laboratory performing the test. These tests will become negative in CD patients who are on gluten free diet. Our laboratory specializes in these and experience indicates that one month or longer on a gluten-containing diet should yield positive results in celiac patients. Vijay Kumar, Ph.D., F.A.C.B. IMMCO Diagnostics, Inc. [log in to unmask] 1-800-537-TEST