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An examination of the lower part of the gastrointestinal tract, which is called the colon or large intestine (bowel).

It is a safe procedure that provides information other tests may not be able to give. It is performed by an endoscopist, a physician with special training in endoscopy procedures. The colonoscope is inserted into the anus and advanced through the entire colon (to the cecum) and possibly a short distance into the small intestine. The procedure generally between twenty minutes and one hour.


The most common reasons for colonoscopy are to evaluate the following :

  • As a screening exam for anyone over age 50
  • Blood in the stool or rectal bleeding
  • Dark/black stools
  • Persistent diarrhea
  • Iron deficiency anemia (a decrease in blood count due to loss of iron)
  • Significant, unexplained weight loss, accompanied by gastrointestinal symptoms
  • A family history of colon cancer
  • To follow up an abnormal barium enema
  • A history of previous colon polyps or colon cancer
  • Surveillance in people with ulcerative colitis
  • For the medical management of chronic inflammatory bowel disease
  • Chronic, unexplained abdominal pain.

The endoscopy unit will provide specific instructions about how to prepare for the examination. The instructions are designed to maximize safety during and after the examination, minimize possible complications, and allow the endoscopist to fully view the colon.

It is important to read the instructions ahead of time and follow them carefully; patients who have questions should speak with their healthcare provider or the endoscopy unit.

The inside lining of the colon must be cleaned of stool to permit the endoscopist to complete a thorough examination. This is accomplished by restricting what is eaten and by using purgatives.

What to eat

  • As a general rule, patients should not eat any solid food for at least one day before the examination. Only clear liquids (such as juices without pulp, bouillon, ginger ale) or clear gelatin (flavored is fine, but without added fruit) are recommended.


  • This involves drinking a gallon of an undigestible solution (Fortrans) that causes temporary diarrhea. Drinking such a large volume of cold solution may cause a patient to feel chilled, but the sensation is temporary. Many patients say that drinking the purgative solution is the most unpleasant part of the examination.


  • Some medications, such as aspirin and iron preparations, should be discontinued for one to two weeks before the examination.
  • Patients should also ask about medications for diabetes, heart or lung disease, high blood pressure, or seizure disorders. Some medications should not be stopped, and many of them can be taken the examination.
  • Patients who take antibiotics before dental procedures should ask if they will be needed before colonoscopy.


  • Patients need to arrange for someone to escort them safely home after the examination. Although patients will be awake by the time of discharge, the sedative medications cause changes in reflexes and judgement that cause a person to feel well but can interfere with the ability to make decisions, similar to the effect of alcohol.

Prior to the endoscopy, a nurse will ask questions to ensure the patient understands the procedure and the reason it is planned. The nurse will ask questions to ensure the patient has prepared properly for the procedure. A doctor will also review the procedure, including possible complications, and will ask patients to sign a consent form.

The nurse will start an intravenous line (insert a needle into a vein in the hand or arm) to administer medications. The intravenous line insertion feels like a pin prick, similar to having blood drawn.

The vital signs (blood pressure, heart rate, and blood oxygen level) will be monitored before, during, and after the examination. The monitoring is not painful. Some patients will be given oxygen during the examination.


The colonoscopy will be performed while the patient lies on their left side. Medications will be administered through the intravenous line. Most endoscopy units use a combination of a sedative (to help patients relax), and a narcotic (to prevent discomfort). Many people sleep during the examination while others are very relaxed, comfortable, and generally not aware of the examination.

The colonoscope is a flexible tube, approximately the size of the index finger. It has a lens and a light source that allows the endoscopist to look into the scope or at a TV monitor. The image on the TV monitor is magnified many times so the endoscopist can see small changes in tissue.

The endoscope contains channels that allow the endoscopist to obtain biopsies (small pieces of tissue), remove polyps and to introduce or withdraw fluid or air. Polyps are extra growths of tissue that can range in size from the tip of a pen to several inches (doctors measure them in millimeters and centimeters). Most polyps are benign (not cancerous) but can turn into cancers if left to grow for a very long time. As a result, they are usually removed so they can be analyzed under the microscope. This does not hurt since the lining of the colon does not sense pain.

Air is introduced through the scope to open up the colon so that the scope can be moved forward and to allow the endoscopist to see. Patients may experience a feeling of bloating or gas cramps from the air as it distends the colon. Try not to be embarrassed about releasing the air through the rectum; patients should let their physician know if they are uncomfortable.


After the colonoscopy, a patient will be observed until the effects of the sedative medication are gone.

The most common discomfort after colonoscopy is a feeling of bloating and gas cramps. Patients may also feel groggy from the sedation medications. Patients should not return to work that day. Most patients are able to eat a regular diet after the examination. Patients should ask about when it is safe to restart aspirin or blood thinning medications.


Colonoscopy is a safe procedure and complications are rare, but can occur:

  • Bleeding can occur from biopsies or the removal of polyps, but it is usually minimal and stops quickly or can be controlled.
  • The colonoscope can cause a tear or hole in the tissue being examined, which is a serious problem, but fortunately, very uncommon.
  • Adverse reactions to the medications used to sedate you are possible. The endoscopy team (doctors and nurses) will ask about previous medication allergies or reactions and about health problems such as heart, lung, kidney, or liver disease.
  • The medications can also produce irritation in the vein at the site of the intravenous line. If redness, swelling, or warmth occur, warm to hot wet towels applied to the site may relieve the discomfort. If the discomfort persists, notify the endoscopy unit.

The following symptoms should be reported immediately:

  • Severe abdominal pain (not just gas cramps)
  • A firm, distended abdomen
  • Fever
  • Bleeding greater than a few tablespoons.

Although patients worry about discomforts of the examination, most people tolerate it very well and feel fine afterwards. Some fatigue after the examination is common. Patients should plan to take it easy and relax the rest of the day.

The endoscopist can describe the result of their examination before the patient leaves the endoscopy unit. If biopsies have been taken or polyps removed, the patient should call for results within one to two weeks.