What is a colonoscopy procedure?

A colonoscopy (koh-luh-NAH-skuh-pee) procedure is a medical exam that allows a doctor to look inside the entire large intestine. The procedure enables the physician to see things such as inflamed tissue, abnormal growths, and ulcers. Colonoscopies are most often used to screen for early signs of cancer in the colon and rectum. The procedure can also help with finding the causes of unexplained changes in bowel habits, and to evaluate symptoms such as abdominal pain, rectal bleeding, and weight loss.

What is the colon?

The colon (large bowel or large intestine) is the last portion of your digestive (gastrointestinal) tract. The colon is a hollow tube about 5 feet long that starts at the end of the small intestine and ends at the rectum and anus. Its main function is to store unabsorbed food waste and absorb water and other body fluids before the waste is eliminated as stool.


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A colonoscopy procedure is performed with the patient lying on their left side on the examining table. You will be given pain medication and a sedative to keep you comfortable and help you relax during the procedure.

The doctor will then insert a long, flexible, lighted tube into your rectum and slowly guide it through your colon. The tube is called a colonoscope (koh-LON-oh-skope). The scope has a camera on its tip that transmits an image of the inside of the colon onto a video screen so the doctor can carefully examine the colon’s lining. The device also bends so that the doctor is able to move it around the curves of the colon.  By blowing air into the colon and inflating it, the tube helps give the doctor a better view. Gentle abdominal pressure is often used to help guide the scope.

A doctor can remove polyps during a colon cancer-screening colonoscopy using tiny tools passed through the scope. Polyps are abnormal growths in the lining of the bowel. Over time some polyps can evolve into colon cancer, which is why collected polyps are sent to a lab for testing. By identifying and removing polyps, a colonoscopy can prevent most cancers from forming.

The doctor can also remove tissue samples to test in the lab for diseases of the colon (biopsy).  If bleeding is found during a colonoscopy procedure, the doctor can pass a laser, heater probe, electrical probe, clipping device, or special medicine through the scope to stop it. The tissue removal and treatments to stop bleeding usually do not cause pain. In many cases, colonoscopies allow for accurate diagnosis and treatment of abnormalities in the colon without the need for major operation.

History has proven colonoscopy to be a very safe procedure. Although bleeding and puncture of the colon are possible complications, they are very uncommon.

A colonoscopy procedure usually takes 30 to 60 minutes. The sedative and pain medicine should keep you from feeling most discomfort during the exam. The majority of patients do not remember the exam at all. Afterwards, you may feel some cramping or experience the sensation of having gas, but this usually subsides within an hour. You will need to remain at the colonoscopy facility for 1 to 2 hours until the sedative wears off.

Rarely do people experience severe abdominal pain, fever, bloody bowel movements, dizziness, or weakness following a procedure. If you have any of these side effects, contact your physician immediately.  Make sure to read your discharge instructions carefully. Medications such as blood-thinners may need to be temporarily avoided after undergoing a colonoscopy – especially if a biopsy was performed, or if polyps were removed.  However, achieving full recovery and returning to your regular activities the next day is normal, and even expected.

Reprinted and modified from the National Digestive Diseases Information Clearinghouse.