- Related Topics:
- colorectal cancer
- enema
- rectum
- colon
- colonoscope
- On the Web:
- National Center for Biotechnology Information - Colonoscopy (Oct. 23, 2026)
colonoscopy
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What is a colonoscopy?
A colonoscopy is a medical examination where a doctor uses a narrow, flexible, lighted tube with a tiny video camera, called a colonoscope, to view the interior of the colon, rectum, and anus. It's used to screen for colon and rectal cancer, look for the causes of abdominal pain, and identify ulcers or other abnormalities. During the procedure, the doctor may remove polyps and take tissue samples for examination.
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Why do doctors perform colonoscopies?
Doctors perform colonoscopies as a screening tool for colon and rectal cancer, which often show no symptoms. Colonoscopies help assess patients with abdominal pain, cramps, chronic diarrhea, constipation, blood in the stool, and unexplained weight loss. They can help diagnose inflammatory bowel disease, such as Crohn disease and ulcerative colitis, as well as ulcers, perforations, diverticulitis, and ischemic colitis.
During the procedure, doctors look for and remove polyps, irritated or swollen tissue, signs of cancer, ulcers, and other abnormalities. They may also take tissue samples, called biopsies, or perform treatments such as placing stents, injecting medications, closing wounds, and removing blockages. Doctors recommend colonoscopies every 10 years for people 45–75 years old at average risk of colorectal cancer.
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How is a colonoscopy done?
A colonoscopy is a medical procedure where a doctor examines the interior of the colon, rectum, and anus using a colonoscope, a narrow, flexible, lighted tube with a tiny video camera that transmits images of the colon to a monitor.
During the procedure, the patient receives sedatives and pain medication while the gastroenterologist inserts the colonoscope through the anus into the rectum. The colon is inflated with air, carbon dioxide, or water to improve visibility. The gastroenterologist looks for abnormalities, such as polyps, irritated tissue, or signs of cancer, and can remove polyps or take biopsies using instruments inserted through the colonoscope.
Before a colonoscopy, patients are usually advised to follow a low-fiber diet for a few days and a clear liquid diet the day before. They also need to use a laxative to clean out their colons.
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What does the doctor look for during a colonoscopy?
During a colonoscopy, the gastroenterologist looks for irregularities, such as polyps, irritated or swollen tissue, signs of cancer, and ulcers. If any are found, the doctor will remove polyps and may take tissue samples, called biopsies. The physician may also perform treatments, such as placing stents, injecting medications, closing wounds, and removing blockages.
Colonoscopies can also help physicians diagnose inflammatory bowel disease, including ulcerative colitis and Crohn's disease, perforations, diverticulitis, and ischemic colitis.
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What do patients need to do to prepare for a colonoscopy?
To prepare for a colonoscopy, patients need to follow a specific diet and bowel preparation plan. Typically, doctors advise patients to consume low-fiber foods for several days before the procedure and switch to a clear liquid diet the day before. It's also necessary to clear the colon using a laxative, as any remaining stool can obstruct the video camera's view.
Patients should also discuss their current medications with their doctor to determine if they need to be temporarily stopped or adjusted before the colonoscopy.
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What are the possible risks or side effects of a colonoscopy?
A colonoscopy is a procedure where a gastroenterologist examines the colon for abnormalities, such as polyps, irritated tissue, or signs of cancer. During the procedure, the patient receives sedatives and pain medication while the colonoscope is inserted through the anus into the rectum. The doctor may remove polyps or take biopsies using instruments inserted through the colonoscope.
Though rare, colonoscopy risks include abnormal reactions to sedatives, bleeding from polyp removal or biopsy, colon or rectum wall perforation, and infection. If the colonoscopy results are negative, another one may be recommended in 10 years. If polyps or abnormal tissues are found, treatment or more frequent colonoscopies may be necessary.
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colonoscopy, a medical examination of the interior of the colon (large intestine), rectum, and anus, by the insertion of a narrow, flexible, lighted tube called a colonoscope. A tiny video camera on the end of the tube transmits images of the colon to an external monitor. A colonoscopy, which is a type of endoscopy, can be used as a screening, diagnostic, or therapeutic tool.
Uses
One of the most important uses of colonoscopy is as a screening tool for colon cancer and rectal cancer (also called colorectal cancer). This type of cancer, which usually develops from abnormal growths called polyps, often has no symptoms. Most polyps are benign, but some are precancerous. Colonoscopies are also used to assess patients with symptoms such as abdominal pain, cramps, chronic diarrhea, constipation, incontinence, blood in the stool, and unexplained weight loss. A colonoscopy can help physicians diagnose inflammatory bowel disease, including Crohn disease and ulcerative colitis; ulcers; perforations; diverticulitis; and intestinal ischemia and ischemic colitis.
Testing demographics
Physicians recommend that people who are 45–75 years old and at average risk of colorectal cancer get a colonoscopy every 10 years. Risk factors include smoking, obesity, having a family history of colorectal polyps or colorectal cancer, having a personal history of inflammatory bowel disease, and having hereditary nonpolyposis colorectal cancer (HNPCC, also known as Lynch syndrome) or familial adenomatous polyposis (FAP). After age 75, physicians may or may not recommend further screening for colorectal cancer, depending on a patient’s health and screening history.
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Preparation and procedure
During a colonoscopy, a gastroenterologist looks for polyps, tissue that is irritated or swollen, signs of cancer, ulcers, and other abnormalities and will remove all polyps that they find and may also take other tissue samples called biopsies. The gastroenterologist may also perform other treatments during a colonoscopy, including placing stents, injecting medications, closing wounds, and removing blockages.
The patient is given sedatives—either general anesthesia or medications that induce conscious sedation—and pain medication, and the gastroenterologist inserts the colonoscope through the anus into the rectum. Air, carbon dioxide, or water are pumped into the colon through a channel in the colonoscope in order to inflate the colon and make it easier to examine. Other medical instruments can be inserted through the channel in the colonoscope to remove polyps or to take biopsies. Complications associated with colonoscopy, which are rare, include abnormal reactions to sedatives, bleeding caused by polyp removal or biopsy, perforation of the colon or rectum wall, and infection. If the results of a colonoscopy are negative, no abnormal tissue was found, and another colonoscopy may be recommended in 10 years if the patient is at average risk for colorectal cancer and has no risk factors other than age. A positive result indicates that polyps or abnormal tissues were detected, which may lead to treatment for a condition; additional colonoscopies may also be recommended within 10 years.
Physicians usually ask patients to eat low-fibre foods for a few days before a colonoscopy and to stick to a clear liquid diet the day before the procedure. Additionally, patients must clean out their colons with a laxative, because stool may block the video camera. Patients should consult with their physician about medications that they take regularly to determine whether they should temporarily stop taking them or adjust the dosages before the procedure.