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 will usually be given medicine into a vein to help you relax. You should not feel any discomfort. You will be awake during the test and may even be able to speak, but you probably will 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 advanced 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.
The health care provider gets a better view as the colonoscope is moved back out. Therefore, a more careful exam is done while the scope is being pulled back. The doctor may take tissue samples with tiny biopsy forceps inserted through the scope. Polyps may be removed with snares, and images may be taken.
Specialized procedures, such as laser therapy, may also be done.
How to Prepare for the Test
You will need to completely cleanse your intestines. 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 give you the steps for cleansing your intestines. This may include using 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
- Sports drinks
- Strained fruit juices
You will usually 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 okay to continue. Iron can make your stool dark black, which 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.
You may have mild abdominal cramping and pass a lot of gas after the exam.
Why the Test is Performed
Colonoscopy may be done for the following reasons:
- Abdominal pain, changes in bowel movements, or weight loss
- Abnormal changes (such as polyps) found on sigmoidoscopy or x-ray tests (CT scan or barium enema)
- Anemia due to low iron (usually when no other cause has been found)
- Blood in the stool, or black, tarry stools
- Follow-up of a past finding, such as polyps or colon cancer
- Inflammatory bowel disease (ulcerative colitis and Crohn's disease)
- Screening for colorectal cancer
Normal findings are healthy intestinal tissues.
What Abnormal Results Mean
- 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 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
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.
Pasricha PJ. Gastrointestinal endoscopy. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 136.
George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon.
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