What is a colonoscopy?

Colonoscopy is a commonly performed procedure used to see inside the colon and rectum. The majority of colonoscopy is performed to screen for and prevent colon cancer. This is accomplished by removing very common (40% of men and 35% of women) precancerous growths of the colon called polyps during the procedure, preventing them from ever turning into a future cancer. Diagnostic colonoscopy is performed for patients experiencing symptoms such as unexplained changes in bowel habits, abdominal pain, bleeding from the anus, and weight loss. In this setting colonoscopy is being performed to look for causes of symptoms such as inflammation, ulcers, and cancer so that appropriate treatment may be offered.

At what age should routine colonoscopy begin?

Routine colonoscopy to prevent cancer by finding and removing polyps should begin at age 45 for most people—earlier if there is a family history of colorectal cancer, a personal history of inflammatory bowel disease, or other risk factors.

What are the colon and rectum?

The colon and rectum are the two main parts of the large intestine. Although the colon is only one part of the large intestine, because most of the large intestine consists of colon, the two terms are often used interchangeably. The large intestine is also sometimes called the large bowel. Digestive waste enters the colon from the small intestine as a semisolid. As waste moves toward the anus, the colon removes moisture and forms stool. The rectum is about 6 inches long and connects the colon to the anus. Stool leaves the body through the anus. Muscles and nerves in the rectum and anus control bowel movements.

How to Prepare for Colonoscopy

The doctor’s office provides written instructions about how to prepare for colonoscopy, also available on the website. The process is called a bowel prep. Generally, all solids must be emptied from the gastrointestinal tract by following a clear liquid diet for the day before the procedure. Patients should not drink beverages containing red or purple dye. Acceptable liquids include

  • fat-free bouillon or broth
  • fruit juice without pulp
  • water
  • plain coffee
  • plain tea
  • sports drinks, such as Gatorade
  • gelatin

The bowel preparation typically starts the evening before the colonoscopy. There is often a second portion on the day of the procedure. The bowel preparation loosens stool and increases bowel movements, ultimately producing an complete emptying of the colon. Your bowel prep may either be in the form of tablets or liquid. Either way, there is a fair volume of fluid intake needed along with the medication portion of the preparation in order to fully flush the colon.

Patients should inform the doctor of all medical conditions and any medications, vitamins, or supplements taken regularly, including

  • aspirin
  • arthritis medications
  • blood thinners
  • fish oil
  • diabetes medications

Driving is not permitted for 24 hours after colonoscopy to allow the sedative time to wear off. Before the appointment, patients should make plans for a ride home that must be with a known acquaintance or hired medical transport (not taxicab, uber, etc).

How is colonoscopy performed?

Examination of the Large Intestine

During colonoscopy, patients lie on their left side on an examination table. In most cases some form or anesthetic is used. The doctor and medical staff monitor vital signs and attempt to make patients as comfortable as possible.

The doctor inserts flexible, lighted tube called a colonoscope, or scope, into the anus and carefully guides it through the rectum and colon. The scope inflates the large intestine with carbon dioxide gas to give the doctor a better view. A small camera mounted on the scope transmits a high-definition image from inside the large intestine to a video monitor, allowing the doctor to carefully examine the intestinal lining.

Once the scope has reached the beginning of the colon, it is slowly withdrawn and the lining of the large intestine is carefully examined again. Bleeding and puncture of the large intestine are possible but very uncommon complications of colonoscopy.

Removal of Polyps and Biopsy

A doctor can remove growths, called polyps, during colonoscopy and later test them in a laboratory for signs of cancer. Polyps are common in adults and are usually harmless and cause no symptoms. However, most colorectal cancer begins as a polyp, so removing polyps early is an effective way to prevent cancer.

The doctor can also take samples from abnormal-looking tissues during colonoscopy. The procedure, called a biopsy, allows the doctor to later look at the tissue with a microscope for signs of disease.

The doctor removes polyps and takes biopsy tissue using tiny tools passed through the scope. Biopsy of the colon and removal of polyps does not result in any pain following the procedure.


Colonoscopy usually takes 15 to 30 minutes. Cramping or bloating may be experienced during the first hour after the procedure but tends to dissipate very quickly. The sedative takes time to completely wear off. Patients are typically monitored while waking up fully for about 1 hours after the procedure. Full recovery is expected by the next day. Discharge instructions should be carefully read and followed. There are usually no activity restrictions the day following the procedure. Patients are generally permitted to return to their normal diet immediately following the procedure.

Patients who develop any of these rare side effects should contact their doctor immediately:

  • severe abdominal pain
  • fever
  • bloody bowel movements
  • dizziness
  • weakness

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