What Is It?

Colonoscopy is an examination of your colon, including higher areas that are beyond the reach of sigmoidoscopy. To perform this exam, your doctor uses a colonoscope. This is a flexible viewing tube with lenses, a small TV camera and a light on one end. Through bundles of flexible glass fibers (fiber-optic technology) and a small video computer chip, the colonoscope scans the inside of your colon and transmits images to a video screen.

During colonoscopy, your doctor can check your colon for cancer, sites of bleeding, ulcers and abnormal growths called polyps, which usually can be removed during the colonoscopy. The procedure may take up to one and a half hours and is performed in your doctor’s office or an ambulatory suite of a hospital. Although the colonoscope is lubricated and bends easily, you will be lightly sedated to minimize any discomfort.

What It’s Used For

Colonoscopy is used to visualize the lining of your colon. This makes it useful in detecting colon cancer, ulcers, inflammation and other problems of the gastrointestinal tract. For routine screening, your doctor will recommend sigmoidoscopy every three to five years, beginning at age 50, or colonoscopy every 10 years. Both sigmoidoscopy and colonoscopy should begin earlier in persons with a high risk of colorectal cancer due to a family history of colorectal cancer, chronic inflammatory bowel disease or certain hereditary syndromes, including familial adenomatous polyposis. More frequent colonoscopy also is recommended for anyone who has already had either a cancerous growth or adenomatous polyp removed from the bowel.

Colonoscopy may be performed as a follow-up exam after a positive fecal occult blood test. It also can be used to identify the source of rectal bleeding or to confirm that there are areas of colitis (inflammation of the colon) in someone who has symptoms.

If your doctor sees a suspicious area during colonoscopy, he or she can use an attachment at the end of the colonoscope to take a biopsy (small tissue sample) to be sent for laboratory examination. If a polyp is found during colonoscopy, your doctor may use a wire loop attachment to remove the entire polyp so that it can be sent for laboratory analysis.


Your bowel needs to be fairly empty during colonoscopy to give your doctor a clear view of your intestinal wall. To help empty your bowel, your doctor will give you specific directions about using laxatives the day before the procedure. In some cases, you may be asked to use an enema the day of the procedure. You will also need to follow a liquid diet for one to two days before the procedure with a full fast (nothing by mouth) after midnight of the evening before. Your doctor will give you more exact details about diet when you schedule your colonoscopy exam. Because you will receive medication during colonoscopy that may make you feel drowsy, arrange for a friend or family member to help you get home from the doctor’s office.

How It’s Done

You will put on a hospital gown, and the doctor’s assistant will record your temperature, pulse, blood pressure and respiratory rate (number of breaths per minute). A pulse oximeter (to measure the oxygen saturation level of your blood) may be placed on your finger, ear or toe, and electrocardiograph (EKG) recording patches will be placed on your chest to monitor your heartbeat. You will be asked to lie on your side on an examination table, with the lower portion of your body covered by a sheet. As your doctor directs, you may be asked to raise one or both of your knees up to your chest. You will be given medication that will lightly sedate you and limit any discomfort caused by the colonoscopy exam. You may be asked to facilitate the insertion of the colonoscope during the examination. The doctor will insert a lubricated, flexible colonoscope into your rectum and, as necessary, pump a small amount of air through the colonoscope to open up your intestinal passage for a clearer view. Your doctor may also take a stool sample or biopsy from inside your bowel.


After colonoscopy is done, you can get dressed. However, because you may still feel drowsy from the medication, a friend or family member should help you get home. You may return to your normal diet whenever you wish. If your doctor took a stool sample or biopsy during the exam, check back in a few days for the results.


Although it is possible that your bowel might be injured or punctured during colonoscopy, this is an uncommon complication.

When To Call A Professional

Call your doctor immediately if you see rectal bleeding after colonoscopy, or if you feel faint, dizzy, short of breath or have palpitations. Also call your doctor if you have nausea, vomiting, cramps or any other type of abdominal pain, or if you develop a fever, chills, severe headache or muscle aches.

If you are a woman who has a history of ovarian, endometrial or breast cancer, your doctor may recommend more frequent colonoscopy, since there is some evidence that your risk of colorectal cancer may be higher than average.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.