It is important to remember that most patients with abdominal pain, bloating or diarrhea do not have celiac disease. In order to test for celiac disease with blood tests and/or endoscopy, the doctor should suspect celiac disease as the cause for the symptoms. When the doctor thinks that celiac disease is possible, but not very likely, then blood tests alone are done. If the blood tests are normal, other tests are rarely necessary. Sometimes the doctor strongly suspects that the symptoms are due to celiac disease or another similar illness, and will request an endoscopy and biopsy (sampling of the tissue of the small intestine). All tests for celiac disease, except for genetic tests, must be done while the patient is on a normal diet that contains gluten. Patients who are concerned that they may have celiac disease should not restrict their diet prior to seeking medical evaluation because this may cause false negative test results.
Specific antibody blood tests are used to diagnose patients with CD. These blood tests are also used to test people who may be at risk for having CD but have no symptoms (relatives of patients with CD). The 2 most accurate tests used are the endomysial antibody and tissue transglutaminase antibody tests. Other tests, such as tests for deamidated gliadin peptide antibodies, may be used in restricted circumstances, but are not as accurate because they can be abnormal in healthy patients who do not have celiac disease or in people with other digestive problems. The original anti-gliadin or anti-gluten tests are no longer used for the diagnosis of celiac disease. Other tests for allergies will not detect celiac disease. Tests on saliva or stool for antibodies are not good substitutes for the blood-based tests. Genetic tests are available to assist doctors when the blood tests are unclear, or when patients continue to have symptoms while on a gluten free diet. However, simply carrying the genes that enable celiac disease does not mean that the patient will get celiac disease, only that it is possible. Not having the genes is a very good way to rule out the possibility of having celiac disease and may be used when the certainty of diagnosis is in doubt.
Establishing a firm diagnosis of CD requires taking biopsy samples of the small intestine using endoscopy. Endoscopy involves insertion of a thin flexible tube through the mouth into the stomach and small intestine. Tiny samples are taken from the wall of the small intestine and are examined under a microscope for changes of CD. This test is usually performed with the aid of sedatives.