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A Dark View Becomes Known


A colonoscopy is a procedure whereby an internal examination of the colon (also known as the large intestine) is performed. By inserting a colonoscope – a long, flexible viewing tube with a small camera attached to it – into the rectum, an inspection of the inside of the entire colon is possible.

Why Is a Colonoscopy Performed?

A colonoscopy is also performed to

  • Determine the type and extent of inflammatory bowel disease (Crohn’s disease and ulcerative colitis);
  • Evaluate abdominal pain, abnormalities (such as polyps) found on contrast X-rays (barium enema), persistent diarrhea, or unexplained blood in the stool;
  • Follow-up a previous finding of colon cancer, or a family history of colon cancer;
  • Investigate the cause of unexplained anemia;
  • Obtain a tissue sample for a biopsy; and
  • Screen for colon cancer. For example, if a polyp or cancer is found in a sigmoidoscopy screening, a complete colonoscopy is performed as a cancer preventative.

Only a colonoscopy enables the health care provider to see the entire length of the colon (four or five feet) unlike a sigmoidoscopy, which can examine only the lower third of the colon (the final two feet). In addition, if colon polyps are found during a colonoscopy, those smaller than one millimeter can be removed during the examination with the colonoscope and sent to a pathologist.

The majority of polyps removed during a colonoscopy are benign. Many are pre-cancerous, however, and their early removal ensures that the polyps do not have the opportunity to develop into colon cancer in the future.

How Is a Colonoscopy Performed?

Once a pain reliever and sedative has been administered, the patient lies on her/his left side, drawing the knees toward the chest. The first step of the procedure is often a digital rectal examination to assess the tone of the sphincter, and confirm that preparation has been adequate.

The colonoscope is inserted through the anus, and gently advanced up the rectum, through the colon, eventually reaching its destination at the ileum. The colonoscope has channels for instrumentation, air, suction, and light. The bowel is occasionally bathed with air to facilitate visibility.

A more thorough examination is performed during withdrawal of the colonoscope since better views are available during this part of the procedure than while the instrument is being inserted.

Small polyps are removed during the examination should any be discovered. In addition, tiny biopsy forceps can be inserted through the colonoscope if tissue samples are required.

Preparing for a Colonoscopy

The colon must be clear of stool and fluids for the colonoscopy to be accurate. Patients are normally asked to do the following during the twenty-four hours preceding the exam:

  • Stop taking iron pills or medications containing iron, as iron residues produce a dark black stool, which interferes with a clear view.
  • Take laxatives and sometimes enemas.
  • Avoid eating solid foods; eat only soft foods.
  • Fasting on exam day may be required.
  • Drink only clear, non-alcoholic liquids such as black coffee, tea, water, or clear broth and juices.
  • Avoid liquids that are red in color, as they can be confused with blood in the colon.
  • Drink plenty of clear liquids to avoid dehydration.

Note that if you have diabetes or take blood thinners, including aspirin or other pain relievers, your preparation for colonoscopy may be slightly different.

What to Expect – Does a Colonoscopy Hurt?

A colonoscopy takes an average of twenty to thirty minutes, depending on what is discovered. When performed by an experienced health care practitioner, the procedure can be painless.

Because the exam causes considerable anxiety for many people, and pain for others, some form of anesthesia or sedation is provided. A sedative together with pain medication enables people to better tolerate the procedure, and the drugs induce relaxation and drowsiness.

Discomfort can be further reduced by taking slow, deep breaths during the procedure. This can help to relax the abdominal muscles, enabling the colonoscopy to progress more easily.

A rectal examination is normally carried out prior to the colonoscopy to dilate the rectum, and ensure there is nothing obstructing the passage. It is normal to feel the urge to defecate when the rectal exam is performed or as the colonoscope is inserted.

As the scope moves inside the colon, some people report experiencing the sensation of pressure. Mild cramping and gas pains may occur; flatulence is necessary and ought to be expected.

Some recovery time is necessary after the procedure to allow the sedative wear off. Patients are normally required to have someone accompany them home after the procedure.

The body needs to rest for several hours after the procedure. It is also necessary to drink plenty of fluids afterwards in order to replace those lost as a result of preparatory fasting and laxatives.

A common aftereffect from the colonoscopy is mild abdominal cramping and considerable passing of gas caused by the administration of air into the colon during the procedure.

Risk Factors Associated with Colonoscopy

A gastrointestinal perforation – a tear or hole in the colon’s lining – is the most serious complication that can occur from a colonoscopy. This situation is life-threatening, requiring immediate surgery. The rate of perforation, however, is low at two out of every one thousand tests.1

Persistent bleeding from biopsy or polyp-removal sites occurs in one out of every one thousand tests.2Some complications from bleeding may be treated during the procedure via cauterization. Delayed bleeding may occur at the site of a polyp removal up to a week after the procedure, and can be treated with a repeat of the procedure.

Rarely, splenic rupture can occur because of adhesions between the colon and the spleen.

Adverse reaction to sedative medication, causing breathing problems or low blood pressure, occurs in four out of ten thousand tests.3

While very rare, infection requiring antibiotic therapy can happen.

In some cases, nausea, vomiting, bloating, and/or rectal irritation can be caused by oral medicines taken to cleanse the bowel prior to the procedure.


1. Mediline Plus, Medical Encyclopedia, “Colonoscopy,” United States National Library of Medicine and National Institutes of Health, http://www.nlm.nih.gov/medlineplus/ency/article/000262.htm (accessed December 4, 2007).
2. Ibid.
3. Ibid

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