DIGESTIVE DISEASE CENTER | Gastroenterology home | Surgery home

Patient care — diagnostic tools, tests, procedures


Definition: A colonoscopy is a procedure for viewing the interior lining of the large intestine (colon) using a small camera called a colonoscope (which is a flexible fiber-optic tube).

How the test is performed: You lie on your left side with your knees drawn up toward the abdomen. After administration of an intravenous sedative and analgesic, the instrument is inserted through the anus and gently advanced under direct vision to the terminal small bowel.

Air will be inserted through the scope to provide a better view. Suction may be used to remove secretions.

Since better views are obtained during withdrawal than during insertion, a more careful examination is done during withdrawal of the scope. Tissue samples may be taken with tiny biopsy forceps inserted through the scope. Polyps can be removed with electrocautery snares, and photographs can be taken.

Specialized procedures, such as laser therapy, can also be performed.

There are 3 basic tests for colon cancer: a stool test (to check for blood); sigmoidoscopy (inspection of the lower colon; and colonoscopy (inspection of the entire colon). All 3 are effective in catching cancers in the early stages, when treatment is most beneficial.

A sample of colon tissue is obtained during a colonoscopy procedure using special instruments. The specimen is sent to the laboratory and placed in a culture media. The specimen is examined daily for the presence of microorganisms.

How to prepare for the test: Thorough cleansing of the bowel is mandatory. Instructions for doing so will be given by the health care provider. This will include using enemas, abstaining from all solid foods 2 or 3 days before the test, and taking laxatives.

To avoid dehydration, drink plenty of clear liquids (such as juices and broths). Unless otherwise instructed, continue taking any regularly-prescribed medication. Discontinue taking iron preparations a few weeks before the test, unless otherwise instructed by the health care provider (iron residues produce a dark black stool, which inhibits the view).

Complete emptying of the colon before the examination requires enemas or other purgatives. These must be repeated until no solid matter remains. An intravenous infusion and an injection will be given to administer a pain reliever and a sedative during the procedure.

People with valvular heart disease may receive antibiotics before and after the test to prevent infection. Outpatients must plan to have someone take them home after the test, as they will be woozy and unable to drive.

How the test will feel: The sedative and pain medication will provide relaxation and produce a drowsy feeling. A rectal examination usually precedes the test to dilate the rectum and make sure there are no major obstructions. You may have the urge to defecate when the rectal exam is performed or as the colonoscope is inserted.

You may feel pressure as the scope moves inside. Brief cramping and gas pains may be experienced as air is inserted or as the scope advances. The passing of gas is necessary and should be expected.

Discomfort may be lessened by taking slow, deep breaths. This will also help relax the abdominal muscles. Mild abdominal cramping and considerable passing of gas may occur after the exam. Medications will produce sedation, which should wear off in a few hours.

Why the test is performed:

  • to obtain tissue specimen for biopsy
  • to evaluate unexplained blood in the stool, abdominal pain, persistent diarrhea, or abnormalities (such as polyps) found on contrast X-rays (barium enema)
  • to determine the type and extent of inflammatory bowel disease (ulcerative colitis and Crohn's disease)
  • to follow people with previous polyps, colon cancer, or a family history of colon cancer

Normal Values: Normal findings are simply healthy intestinal tissues.

What abnormal results mean:

  • lower gastrointestinal (GI) bleeding
  • polyps (which can be removed through the colonoscope during the exam)
  • tumor
  • inflammatory bowel disease
  • diverticulosis (particularly in older people)

Additional conditions under which the test may be performed:

  • CMV gastroenteritis/colitis
  • colon cancer screening
  • colorectal polyps
  • ischemic colitis
  • pseudomembranous colitis

What the risks are:

  • bowel perforation, requiring an operation to repair the hole (less than 2 out of 1,000 tests)
  • heavy or persistent bleeding from biopsy or polypectomy sites (1 out of 1,000 tests)
  • adverse reaction to sedative medication causing respiratory depression or low blood pressure (4 out of 10,000 tests)
  • infection requiring antibiotic therapy (very rare)
  • nausea, vomiting, bloating, and rectal irritation caused by oral purgatives

Special considerations: You must sign an informed consent form. Several hours rest is recommended after the test. To replace fluids lost because of laxatives and fasting, drink plenty of liquids after the test.

Return to diagnostic tools, tests page