Colonoscopy lets the physician look inside your entire large intestine, from the lowest part, the rectum, all the way up through the colon to the lower end of the small intestine. The procedure is used to look for early signs of cancer in the colon and rectum. It is also used to diagnose the causes of unexplained changes in bowel habits. Colonoscopy enables the physician to see inflamed tissue, abnormal growths, ulcers, and bleeding.

For the procedure, you will lie on your left side on the examining table. You will probably be given pain medication and a mild sedative to keep you comfortable and to help you relax during the exam. The physician will insert a long, flexible, lighted tube into your rectum and slowly guide it into your colon. The tube is called a colonoscope (koh-LON-oh-skope). The scope transmits an image of the inside of the colon, so the physician can carefully examine the lining of the colon. The scope bends, so the physician can move it around the curves of your colon. You may be asked to change position occasionally to help the physician move the scope. The scope also blows air into your colon, which inflates the colon and helps the physician see better.

If anything abnormal is seen in your colon, like a polyp or inflamed tissue, the physician can remove all or part of it using tiny instruments passed through the scope. That tissue (biopsy) is then sent to a lab for testing. If there is bleeding in the colon, the physician can pass a laser, heater probe, or electrical probe, or inject special medicines through the scope and use it to stop the bleeding.

Bleeding and puncture of the colon are possible complications of colonoscopy. However, such complications are uncommon.

Colonoscopy takes 15 to 30 minutes. The sedative and pain medicine should keep you from feeling much discomfort during the exam. You will need to remain at the endoscopy facility for 1 to 2 hours until the sedative wears off.