A colonoscopy is an internal examination of the colon (large intestine) and rectum, using an instrument called a colonoscope.
How the test is performed
The colonoscope has a small camera attached to a flexible tube. Unlike sigmoidoscopy, which can only reach the lower third of the colon, colonoscopy examines the entire length of the colon.
You will lie on your left side with your knees drawn up toward your chest. After you have received a sedative and pain reliever, the colonoscope is inserted through the anus. It is gently moved into the beginning of the large bowel and sometimes into 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 electrocautery snares, and photographs 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. Your health care provider will give you instructions for doing this. This may include a combination of enemas, not eating solid foods for 2 or 3 days before the test, and taking laxatives. You will usually be told to stop taking aspirin, ibuprofen, naproxen, or other blood-thinning medications for several days before the test.
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
Unless otherwise instructed, continue taking any regularly prescribed medication. Stop taking iron medications 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.
Outpatients must plan to have someone take them home after the test, because they will be woozy and unable to drive.
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:
How the test will feel
The sedative and pain medication will relax you and make you feel drowsy. Many patients do not remember having the colonoscopy. A rectal examination usually is done before the test to make sure there are no major blockages. You may have the urge to have a bowel movement when the rectal exam is performed or as the colonoscope is inserted.
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 can reduce discomfort by taking slow, deep breaths. This will also help relax your abdominal muscles. You may have mild abdominal cramping and pass a lot of gas after the exam. Sedation should wear off in a few hours. Because of the sedation, you may not feel any discomfort and may have no memory of the test.
Why the test is performed
Colonoscopy may be used 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
- Diverticulosis (abnormal pouches on the lining of the intestines, which increase with age)
- Inflammatory bowel disease
- Lower gastrointestinal (GI) bleeding
- Polyps (which can be removed through the colonoscope during the exam)
Additional conditions under which the test may be performed:
What the risks are
- Heavy or persistent bleeding from biopsy or polyp-removal sites
- Hole or tear in the wall of the colon (bowel perforation) that requires a repair operation
- Fluid imbalances in the body due to enemas and laxatives given before the procedure
- Infection needing antibiotic therapy (very rare)
- Nausea, vomiting, bloating, or rectal irritation caused by medicines taken by mouth to cleanse the bowel
- Reaction to sedative medication, causing breathing problems or low blood pressure
You must sign an informed consent form. Several hours of rest is recommended after the test. To replace fluids lost because of laxatives and fasting, drink plenty of liquids 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, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 136.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and 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.