A colonoscopy is an exam that views the inside of the colon (large intestine) and rectum, using a tool called a colonoscope.
The colonoscope has a small camera attached to a flexible tube that can reach the length of the colon.
How the Test is Performed
You are likely given medicine into a vein to help you relax. You should not feel any pain. You are awake during the test and may even be able to speak. But you probably will not remember anything.
You lie on your left side with your knees drawn up toward your chest.
The colonoscope is gently inserted through the anus. It is carefully moved into the beginning of the large intestine. The scope is slowly advanced as far as the lowest part of the small intestine.
Air is inserted through the scope to provide a better view. Suction may be used to remove fluid or stool.
The doctor gets a better view as the scope is moved back out. Therefore, a more careful exam is done while the scope is being pulled back.
Tissue samples (biopsy) or polyps may be removed using tiny tools inserted through the scope. Photos may be taken using the camera at the end of the scope. If needed, procedures, such as laser therapy, are also done.
How to Prepare for the Test
Your bowel needs to be completely empty and clean for the exam. A problem in your large intestine that needs to be treated may be missed if your intestines are not cleaned out.
Your health care provider will give you the steps for cleansing your bowel. This is called bowel preparation. Steps may include using enemas, not eating solid foods for 2 or 3 days before the test, and taking laxatives.
You need to drink plenty of clear liquids for 1 to 3 days before the test. Examples of clear liquids are:
Clear coffee or tea
Fat-free bouillon or broth
Strained fruit juices
You will likely be told to stop taking aspirin, ibuprofen, naproxen, or other blood-thinning medicines for several days before the test. Keep taking your other medicines unless your doctor tells you otherwise.
You will need to stop taking iron pills or liquids a few days before the test, unless your health care provider tells you it is OK to continue. Iron can make your stool dark black. This makes it harder for the doctor to view inside your bowel.
How the Test will Feel
The medicines will make you sleepy so that may not feel any discomfort or have any 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.
After the exam, you may have mild abdominal cramping and pass a lot of gas. You may also feel bloated and sick to your stomach. These soon go away.
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 important decisions for at least 24 hours after the test.
Why the Test is Performed
Colonoscopy may be done for the following reasons:
Abdominal pain, changes in bowel movements, or weight loss
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 disease, ulcerative colitis, infection, or lack of blood flow
Small growths called polyps on the lining of your colon (which can be removed through the colonoscope during the exam)
Heavy or ongoing bleeding from biopsy or removal of polyps
Hole or tear in the wall of the colon that requires surgery to repair
Infection needing antibiotic therapy (very rare)
Reaction to the medicine you take to relax, causing breathing problems or low blood pressure
Kimmey MB. Complications of gastrointestinal endoscopy. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology/Diagnosis/Management. 9th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 40.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Colorectal cancer screening. Version 2.2013. Available at: http://www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Accessed October 24, 2013.
George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.