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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

Colonoscopy is done most often in a procedure room at your doctor's office. It can also be done in the outpatient department of a hospital or medical center.

  • You are likely given medicine into a vein (IV) to help you relax. You should not feel any pain. You are awake during the test and may even be able to speak. You will probably 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. So, 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
  • 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
  • Gelatin
  • Sports drinks without added color
  • Strained fruit juices
  • Water

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 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 you 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 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 providers 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:

Normal Results

Normal findings are healthy intestinal tissues.

What Abnormal Results Mean

Abnormal test results may mean any of the following:

  • 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)


Risks of colonoscopy may include any of the following:

  • 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 are given 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.

Lieberman DA, Rex DK, Winawer SJ, et al.; United States Multi-Society Task Force on Colorectal Cancer. Guidelines for colonoscopy surveillance after screening and polypectomy: a consensus update by the US Multi-Society Task Force on Colorectal Cancer. Gastroenterology. 2012;143:844-857. PMID 22763141. Available at:

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Colorectal cancer screening. Version 1.2014. Available at: Accessed February 12, 2015.

Pasricha PJ. Gastrointestinal endoscopy. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 136.

U.S. Preventive Services Task Force. Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2008;149:627-637. PMID 18838716. Available at:

Review Date: 2/11/2015
Reviewed By: Subodh K. Lal, MD, gastroenterologist at Gastrointestinal Specialists of Georgia, Austell, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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