Irritable bowel syndrome (IBS) is generally diagnosed on the basis of a complete medical history that includes a careful description of symptoms and a physical examination.
Although there is no specific test for IBS, diagnostic tests may be performed to rule out other problems. These tests may include stool sample testing, blood tests, and x-rays. Typically, a doctor will perform a sigmoidoscopy, or colonoscopy, which allows the doctor to look inside the colon. This is done by inserting a small, flexible tube with a camera on the end of it through the anus. The camera then transfers the images of your colon onto a large screen for the doctor to see.
If your test results are negative, the doctor may diagnose IBS based on your symptoms, including how often you have had abdominal pain or discomfort during the past year, when the pain starts and stops in relation to bowel function, and how your bowel frequency and stool consistency have changed.