How is irritable bowel syndrome (IBS) diagnosed?

When you see your doctor about irritable bowel syndrome (IBS), he or she will take your medical history and perform a physical examination. Depending on your symptoms, your doctor may want to run certain tests in order to make a diagnosis, including blood tests and stool samples. These tests are usually normal, but they rule out other diseases which may mimic IBS.

Depending on the symptoms and other pertinent factors in the medical history, your doctor may perform a procedure called flexible sigmoidoscopy. Flexible sigmoidoscopy is a routine outpatient procedure in which the inside of the lower large intestine is examined.

Flexible sigmoidoscopies are commonly used to evaluate bowel disorders, rectal bleeding, or polyps (benign growths). During the procedure, a physician uses a sigmoidoscope (a long, flexible instrument about 1/2 inch in diameter) to view the lining of the rectum and lower portion of the colon. The sigmoidoscope is inserted through the rectum and advanced to the descending colon.

Another option for examining the colon is a colonoscopy. Colonoscopy is also an outpatient procedure, similar to a sigmoidoscopy, in which the entire colon is examined with a colonoscope. If necessary during a colonoscopy, small amounts of tissue can be removed for analysis (biopsy) and polyps can be identified and removed. In many cases, colonoscopy allows accurate diagnosis and treatment without the need for a major operation.