In colonoscopy, a flexible, lighted viewing tube (colonoscope) is passed through the anus, rectum, the full length of the large intestine (or colon), and sometimes into the lower part of the small intestine. The colonoscope is equipped with fiberoptic cables that enable a physician to visually inspect the lining of these organs for any evidence of disease or abnormality. In addition, instruments may be passed through the scope to obtain tissue biopsies or stool samples for microscopic examination.

Colonoscopy is primarily performed in people with symptoms of a bowel abnormality (for example, blood in the stool, recent changes in bowel habits, or abdominal pain) when the cause is unclear or when the results of less invasive tests, such as sigmoidoscopy or barium enema, are negative or inconclusive. It may also be done therapeutically to perform procedures such as polyp removal.

Purpose of the Colonoscopy

  • To detect and evaluate inflammatory or ulcerative bowel disease, colorectal polyps, tumors, bleeding or blood in the stool, abdominal pain, diarrhea and other bowel abnormalities
  • To further evaluate tumors, ulcers, and narrowed passages (strictures) detected by a barium enema
  • To screen for colon cancer or precancerous polyps in people with a high risk of developing the disease, such as those with a strong family history of colorectal cancer or familial polyposis
  • To monitor patients who have been treated for colorectal cancer for recurrence
  • To monitor patients with inflammatory bowel disease for the development of colorectal cancer
  • Used therapeutically to remove polyps, stop active bleeding, dilate narrowed passages, or remove an obstruction

Who Performs Colonoscopy

Special Concerns about Colonoscopy

  • Although colonoscopy may provoke some anxiety, the procedure usually causes only minor discomfort. You will receive a sedative medication before the test.
  • You must wait at least a week after having a barium x-ray procedure before undergoing colonoscopy, since the presence of barium in the abdomen interferes with visual inspection of the colon.
  • Colonoscopy should not be performed in people with a suspected colon perforation or an extremely dilated colon (megacolon), in women who are about to give birth, or in those who have had a recent heart attack or abdominal surgery.
  • The procedure may not be possible in people with painful anorectal conditions such as fissures or hemorrhoids; diverticulitis (inflammation in the sacs of the colon); active bleeding in the bowel or rectum; or acute colon inflammation.
  • Colonoscopy may be performed in a hospital or an outpatient setting.

Before the Colonoscopy

  • Inform your doctor if you regularly take nonsteroidal anti-inflammatory drugs (such as aspirin, ibuprofen, or naproxen) or anticoagulants such as warfarin (Coumadin, Panwarfin). These medications must be discontinued for several days before the test to reduce the risk of bleeding.
  • Cleansing your intestine before colonoscopy is essential to provide clear visibility during the procedure. Your doctor will give you specific instructions.
  • Typically, you should consume only clear liquids (such as water, bouillon, or gelatin) for 24 to 48 hours before the scheduled procedure, and drink large amounts of water on the day before. Do not eat or drink anything after midnight on the day before the test.
  • In addition, your doctor will prescribe an oral laxative agent to take on the day before the procedure. (Sometimes, instead of a laxative, the bowel cleansing is accomplished by drinking a gallon of nonabsorbable salty liquid—for example, GoLYTELY, Colyte, or NuLYTELY.)
  • On the morning of the procedure, a cleansing enema may be administered at the testing facility.
  • Immediately before the test, an intravenous (IV) needle or catheter is inserted into a vein in your arm. A mild sedative medication is usually administered, but you will remain conscious throughout the procedure (so-called conscious sedation).

What You Experience during Colonoscopy

  • You will be asked to wear a hospital gown and remove your eyeglasses.
  • You will be given a pain reliever and IV sedation (a sedative is administered intravenously-through a vein). You will feel relaxed and somewhat drowsy.
  • You lie on your side on a table, with your knees drawn to your chest, and you are draped to minimize any embarrassment.
  • The doctor begins by inserting a gloved, lubricated finger into your rectum to perform a manual examination.
  • Next, the lubricated long, narrow, flexible tube (1/2 inch diameter) is gently inserted through the anus and rectum and into your colon. The scope has a small video camera at the end allowing the doctor to see the inside of your colon on a video monitor.
  • You may experience some abdominal cramping or feel the urge to defecate as the instrument is inserted and advanced. Breathe deeply and slowly through your mouth to relax your abdominal muscles and reduce this discomfort.
  • In order to advance the scope through the deepest portion of the colon, the doctor or a nurse may help you to lie on your back. The doctor may palpate your abdomen or use fluoroscopy to help guide the passage of the scope.
  • As the scope is slowly withdrawn, the doctor carefully inspects the lining of your colon, rectum, and anus, looking for any abnormalities.
  • Small amounts of air will be instilled through the scope to dilate the intestinal passage for better viewing. This may cause you to feel bloated and to pass gas.
  • Depending on the circumstances, a biopsy forceps or other instruments may be inserted through the scope to obtain tissue or stool specimens. Polyps may be entirely removed using an electrocautery device. (These procedures are painless, since the lining of the colon contains no pain receptors.) Tissue and fluid samples will be sent to a laboratory for analysis.
  • The procedure time typically ranges from 30 to 60 minutes.

Risks and Complications of Colonoscopy

  • Possible complications include bleeding, impaired respiration due to oversedation, and, rarely, perforation of the rectum or colon. Perforation requires surgery to repair the hole in the colon.
  • In rare cases, severe abdominal pain, fever, bloody bowel movements, dizziness, or weakness may occur after colonoscopy.If you experience any of these side effects, contact your physician immediately.

After the Colonoscopy

  • You will rest in a recovery room until the sedative wears off (usually about an hour). During this time, your vital signs will be checked periodically, and you will be observed for signs of complications.
  • Arrange for someone to drive you home.
  • You may experience flatulence or gas pains for several hours after the procedure.
  • If a biopsy was performed, you may have a small amount of rectal bleeding for several hours.
  • Rest in bed for the remainder of the day and drink only clear liquids. Do not drink alcohol, drive, or operate machinery for 24 hours following the procedure.
  • After 24 hours, you may resume your normal activities and any medications withheld before the test.
  • Blood may collect and clot under the skin (hematoma) at the IV insertion site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
  • Contact your doctor immediately if you develop fever, chills, excessive rectal bleeding, or abdominal pain or distention.

Colonoscopy Results

  • During the visual inspection of the bowel, the doctor will note any abnormalities such as bleeding, inflammation, abnormal growths, or ulcers.
  • Various laboratory tests may be necessary to pinpoint a diagnosis. For example, biopsied tumors and excised polyps are examined under a microscope by a pathologist for evidence of cancer or another abnormality.
  • If no abnormality is found, your doctor will recommend a schedule of periodic follow-up exams to monitor your health.
  • If a problem is diagnosed based on the findings of this test, appropriate medical or surgical treatment will be recommended.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 05 Jan 2012

Last Modified: 05 Jan 2012