The following tests are useful in diagnosing duodenitis.

• Endoscopy and biopsy: It is the main test used to diagnose duodenitis when people have certain risk factors or when signs and symptoms suggest this disease may be present. After you are sedated (made sleepy), an endoscope which is a thin, flexible, lighted tube was passed down your throat. Then the doctor can view the lining of your esophagus, stomach, and duodenum. The abnormal areas may show as redness, nodules, or eroded areas in the wall of the small intestine. Tissue samples can be obtained through the endoscope and be checked under a microscope to detect the character.
• Blood test, including complete blood count，is needed.
• Stool test: Sometimes occult blood in the stool may be checked.