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Colonoscopy is a medical procedure where a long, flexible, tubular instrument called the colonoscope is used to view the entire inner lining of the colon (large intestine) and the rectum.


A colonoscopy is generally recommended when the patient complains of rectal bleeding or has a change in bowel habits and other unexplained abdominal symptoms. The test is frequently used to test for colorectal cancer, especially when polyps or tumor-like growths have been detected using the barium enema and other diagnostic tests. Polyps can be removed through the colonoscope and samples of tissue (biopsies) can be taken to test for the presence of cancerous cells.
The test also enables the physician to check for bowel diseases such as ulcerative colitis and Crohn's disease. It is a necessary tool in monitoring patients who have a past history of polyps or colon cancer.


The procedure can be done either in the doctor's office or in a special procedure room of a local hospital. An intravenous (IV) line will be started in a vein in the arm. The patient is generally given a sedative and a pain-killer through the IV line.
During the colonoscopy, the patient will be asked to lie on his/her left side with his/her knees drawn up towards the abdomen. The doctor begins the procedure by inserting a lubricated, gloved finger into the anus to check for any abnormal masses or blockage. A thin, well-lubricated colonoscope then will be inserted into the anus and it will be gently advanced through the colon. The lining of the intestine will be examined through the scope. Occasionally air may be pumped through the colonoscope to help clear the path or open the colon. If there are excessive secretions, stool, or blood that obstruct the viewing, they will be suctioned out through the scope. The doctor may press on the abdomen or ask the patient to change his/her position in order to advance the scope through the colon.
The entire length of the large intestine can be examined in this manner. If suspicious growths are observed, tiny biopsy forceps or brushes can be inserted through the colon and tissue samples can be obtained. Small polyps also can be removed through the colonoscope. After the procedure, the colonoscope is slowly withdrawn and the instilled air is allowed to escape. The anal area is then cleansed with tissues.
The procedure may take anywhere from 30 minutes to two hours depending on how easy it is to advance the scope through the colon. Colonoscopy can be a long and uncomfortable procedure, and the bowel cleaning preparation may be tiring and can produce diarrhea and cramping. During the colonoscopy, the sedative and the pain medications will keep the patient very drowsy and relaxed. Most patients complain of minor discomfort and pressure from the colonoscope moving inside. However, the procedure is not painful.
A procedure called virtual colonoscopy has been developed but debate continues on whether or not it is effective as colonoscopy. Virtual colonoscopy refers to the use of imaging, usually with computed tomography (CT) scans or magnetic resonance imaging (MRI) to produce images of the colon. Studies in late 2003 showed that virtual colonoscopy was as effective as colonoscopy for screening purposes and it offered the advantage of being less invasive and less risky. However, many physicians were unwilling to accept it as a replacement for colonoscopy, particularly since some patients might still require the regular colonoscopy as a follow-up to the virtual procedure if a polyp or abnormality is found that requires biopsy.


The doctor should be notified if the patient has allergies to any medications or anesthetics; any bleeding problems; or if the woman is pregnant. The doctor should also be informed of all the medications that the person is currently on and if he or she has had a barium x-ray examination recently. If the patient has had heart valves replaced, the doctor should be informed so that appropriate antibiotics can be administered to prevent any chance of infection. The risks of the procedure will be explained to the patient before performing the procedure and the patient will be asked to sign a consent form.
It is important that the colon be thoroughly cleaned before performing the examination. Before the examination, considerable preparation is necessary to clear the colon of all stool. The patient will be asked to refrain from eating any solid food for 24-48 hours before the test. Only clear liquids such as juices, broth, and gelatin are recommended. The patient is advised to drink plenty of water to avoid dehydration. The evening before the test, the patient will have to take a strong laxative that the doctor has prescribed. Several 1 qt enemas of warm tap water may have to be taken on the morning of the exam. Commercial enemas (e.g., Fleet) may be used.
The patient will be given specific instructions on how to use the enema and how many such enemas are necessary. Generally, the procedure has to be repeated until the return from the enema is clear of stool particles. On the morning of the examination, the patient is instructed not to eat or drink anything. The preparatory procedures are extremely important since, if the colon is not thoroughly clean, the exam cannot be done.
Colonoscopy is a procedure where a long and flexible tubular instrument called a colonoscope is inserted into the patient's anus in order to view the lining of the colon and rectum. It is performed to test for colorectal cancer and other bowel diseases, and enables the physician to collect tissue samples for laboratory analysis.
Colonoscopy is a procedure where a long and flexible tubular instrument called a colonoscope is inserted into the patient's anus in order to view the lining of the colon and rectum. It is performed to test for colorectal cancer and other bowel diseases, and enables the physician to collect tissue samples for laboratory analysis.
(Illustration by Electronic Illustrators Group.)


After the procedure, the patient is kept under observation until the effects of the medications wear off. The patient will have to be driven home by someone and can generally resume a normal diet and usual activities unless otherwise instructed. The patient will be advised to drink lots of fluids to replace those lost by laxatives and fasting.
For a few hours after the procedure, the patient may feel groggy. There may be some abdominal cramping and considerable amount of gas may be passed. If a biopsy was performed or a polyp was removed, there may be small amounts of blood in the stool for a few days. If the patient experiences severe abdominal pain or has persistent and heavy bleeding, it should be brought to the doctor's attention immediately.


The procedure is virtually free of any complications and risks. Very rarely (two in 1000 cases) there may be a perforation (a hole) in the intestinal wall. Heavy bleeding due to the removal of the polyp or from the biopsy site seldom occurs (one in 1000 cases). Infections due to a colonoscopy are also extremely rare. Patients with artificial or abnormal heart valves are usually given antibiotics before and after the procedure to prevent an infection.

Normal results

The results are said to be normal if the lining of the colon is a pale reddish pink and no abnormal looking masses are found in the lining of the colon.

Abnormal results

Abnormal results would imply that polyps or other suspicious-looking masses were detected in the lining of the intestine. Polyps can be removed during the procedure and tissue samples can be biopsied. If cancerous cells are detected in the tissue samples, then a diagnosis of colon cancer is made. The pathologist analyzes the tumor cells further to estimate the aggressiveness of the tumor and the extent of spread of the disease. This is crucial before deciding on the mode of treatment for the disease. Abnormal findings could also be due to inflammatory bowel diseases such as ulcerative colitis or Crohn's disease. A condition called diverticulosis, where many small fingerlike pouches protrude from the colon wall, may also contribute to an abnormal result in the colonoscopy.



"Professional Organization Recommends Standard Colonoscopy Over Virtual." Biotech Week December 31, 2003.
"Study Shows Virtual Colonoscopy as Effective as Traditional Colonoscopy." Biotech Week Dec. 31, 2003.


American Cancer Society. 1599 Clifton Rd., NE, Atlanta, GA 30329-4251. (800) 227-2345.
Cancer Research Institute. 681 Fifth Ave., New York, N.Y. 10022. (800) 992-2623.
National Cancer Institute. Building 31, Room 10A31, 31 Center Drive, MSC 2580, Bethesda, MD 20892-2580. (800) 422-6237.
United Ostomy Association, Inc. (UOA). 19772 MacArthur Blvd., Suite 200, Irvine, CA 92612-2405. (800) 826-0826.

Key terms

Barium enema — An x-ray test of the bowel after giving the patient an enema of a white chalky substance that outlines the colon and the rectum.
Biopsy — Removal of a tissue sample for examination under the microscope to check for cancer cells.
Colonoscope — A thin, flexible, hollow, lighted tube that in inserted through the rectum into the colon to enable the doctor to view the entire lining of the colon.
Crohn's disease — A chronic inflammatory disease where the immune system starts attacking one's own body. The disease generally starts in the gastrointestinal tract.
Diverticulosis — A condition where pouchlike sections that bulge through the large intestine's muscular walls but are not inflamed occur. They may cause bleeding, stomach distress, and excess gas.
Pathologist — A doctor who specializes in the diagnosis of disease by studying cells and tissues under a microscope.
Polyps — Abnormal growths that develop on the inside of a hollow organ such as the colon.
Ulcerative colitis — A chronic condition where recurrent ulcers are found in the colon. It is manifested clinically by abdominal cramping, and rectal bleeding.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


endoscopic examination of the colon, either transabdominally during laparotomy, or transanally by means of a colonoscope.
 Colonoscopy. The endoscopic instrument is passed through the entire colon and into the distal segment of the ileum. The combination of the flexible tube, fiberoptics, and the light enables the examiner to visualize the entire mucosal surface, identifying sites of bleeding, inflammation, tissue irregularity, or abnormal tissue. From Malarkey and McMorrow, 2000.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


Visual examination of the inner surface of the colon by means of a colonoscope.
Synonym(s): coloscopy
[colon + G. skopeō, to view]
Farlex Partner Medical Dictionary © Farlex 2012


n. pl. colonosco·pies
Examination of the colon with a colonoscope. Also called coloscopy.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


GI disease Visualization of the large intestine with a colonoscope; lesions found during colonoscopy are biopsied and examined by a pathologist to determine whether they are benign or malignant Abnormal results GI bleeding, diverticuli, polyps, stricture, tumor, IBD–eg, ulcerative colitis, Crohn's disease Complications Rarely, intestinal perforation. See Virtual colonoscopy.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


Visual examination of the inner surface of the colon by means of a colonoscope.
[colon + G. skopeō, to view]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


An important method of examination of the inside of the COLON, using a steerable, flexible, fibreoptic endoscope which allows meticulous inspection, the taking of biopsies, and, in some cases, treatment.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

Patient discussion about colonoscopy

Q. Why is Colonoscopy Important? I am 60 years old and my doctor recommended that I would do a colonoscopy. She said it is because it's important to do this routinely at this age. Why is it so important?

A. Colonoscopy is a procedure that enables an examiner (usually a gastroenterologist) to evaluate the appearance of the inside of the colon (large bowel). This is accomplished by inserting a flexible tube that is about the thickness of a finger into the anus, and then advancing it slowly, under visual control, into the rectum and through the colon. It is performed with the visual control of either looking through the instrument or with viewing a TV monitor.

This test may be done for a variety of reasons. Most often it is done to investigate the finding of blood in the stool, abdominal pain, diarrhea, a change in the bowel habits, or an abnormality found on colon x- ray or a CT scan. Certain individuals with previous history of polyps or colon cancer and certain individuals with family history of particular malignancies or colon problems may be advised to have periodic colonoscopies because they are at a greater risk of polyps or colon cancer. Hope this helps.

Q. How to prevent diverticulitis? I am a 43 year old man. I just had colonoscopy and my Doctor said I have diverticulosis and am at risk in developing diverticulitis. How can I prevent developing diverticulitis?

A. You have Diverticulosis, which means you have diverticulas (small pouches) on your digestive system. These diverticula are permanent and will not go away. No treatment has been found to prevent complications of diverticular disease. Diet high in fiber increases stool bulk and prevents constipation, and theoretically may help prevent further diverticular formation or worsening of the diverticular condition. Some doctors recommend avoiding nuts, corn, and seeds which can plug diverticular openings and cause diverticulitis. Whether avoidance of such foods is beneficial is unclear. If you develop unexplained fever, chills or abdominal pain, you should notify your doctor immediately since it could be a complication of diverticulitis.

More discussions about colonoscopy
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