A colonoscopy is an internal examination of the colon (large intestine) and rectum, using an instrument called a colonoscope.
The colonoscope has a small camera attached to a flexible tube that can reach and examine the entire length of the colon.
How the test is performed
You will usually be given medicine into a vein to help you relax and not feel any discomfort. You will be awake during the test and may even be able to speak, but you will likely not remember anything.
You will lie on your left side with your knees drawn up toward your chest. The colonoscope is inserted through the anus. It is gently moved into the beginning of the large bowel and slowly moved as far as the lowest part of the small intestine.
Air will be inserted through the scope to provide a better view. Suction may be used to remove fluid or stool.
Because the health care provider gets a better view as the colonoscope is pulled back out, a more careful examination is done while the scope is being pulled out. Tissue samples may be taken with tiny biopsy forceps inserted through the scope. Polyps may be removed with snares, and photographs may be taken.
You will need to completely cleanse your intestines. If you do not do this, a problem in your large intestine that needs to be treated may be missed during the test.
Your health care provider will give you instructions for cleansing your intestines. This may include enemas, not eating solid foods for 2 or 3 days before the test, and taking laxatives.
You will be asked to drink plenty of clear liquids for 1 - 3 days before the test. Examples of clear liquids are:
Clean coffee or tea
Fat-free bouillon or broth
Strained fruit juices
You will usually be told to stop taking aspirin, ibuprofen, naproxen, or other blood-thinning medications for several days before the test. Unless you are told otherwise, continue taking your other medicines.
Stop taking iron pills or liquids a few weeks before the test, unless your health care provider tells you otherwise. Iron can produce a dark black stool, which makes the view inside the bowel less clear.
How the test will feel
Because of the medicines that make you sleepy, you may not feel any discomfort and may have no memory of the test.
You may feel pressure as the scope moves inside. You may feel brief cramping and gas pains as air is inserted or the scope advances. Passing gas is necessary and should be expected.
Abnormal pouches on the lining of the intestines, called diverticulosis
Areas of bleeding
Cancer in the colon or rectum
Colitis (a swollen and inflamed intestine) due to Crohn's disease, ulcerative colitis, infection, or lack of blood flow
Small growths called polyps that stick out of the lining of your colon (which can be removed through the colonoscope during the exam)
What the risks are
Heavy or persistent bleeding from biopsy or polyp-removal sites
Hole or tear in the wall of the colon that requires a repair operation
Infection needing antibiotic therapy (very rare)
Reaction to sedative medication, causing breathing problems or low blood pressure
After the test, you will feel sleepy for a period of time. You may have a headache or feel sick to your stomach or bloated, but this is not common. You may pass a lot of gas.
You should be able to go home about 1 hour after the test. You must plan to have someone take you home after the test, because you will be woozy and unable to drive. The nurses and doctors will not let you leave until someone arrives to help you.
When you are home:
Drink plenty of liquids. Eat a healthy meal to restore your energy.
You should be able to return to your regular activities the next day.
Avoid driving, operating machinery, drinking alcohol, and making legal decisions for at least 24 hours after the test.
Kimmey MB. Complications of gastrointestinal endoscopy. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier;2010:chap 40.
George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.