The Harvard Medical School Family Health Guide
Diagnostic Tests - Colonoscopy
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What happens when the test is performed?
  • You may receive a sedative through an IV (see "Sedatives and anesthesia," page 8). You wear a hospital gown for the test and lie on your side on a table.After putting on a glove and applying some clear jelly to the outside of it, the doctor feels the inside of your rectum with a finger. He or she gently inserts one end of the colonoscope into your rectum. The colonoscope is a type of endoscope that is about half an inch wide and a little more than 5 feet long so it can reach the entire length of your large intestine (see "Endoscopes," page 27).

    The doctor fills your intestine with air so that the camera at the end of the colonoscope gets a good view. If you didn't receive a sedative, you might feel a cramplike pain - similar to the cramping you might get when you have gas-when air is pumped into your colon. Images of the interior of your colon appear on a video screen. If your doctor sees a suspicious place on the bowel lining, he or she might use some small clippers on the end of the scope to take a biopsy.

    If your doctor sees a polyp, he or she removes it with a loop of wire pushed through the colonoscope. The doctor tightens the loop around the polyp's stem and sends a brief electric current through the wire to burn the stem and separate it from your intestine. This process isn't painful because there are few nerve endings in the stem of the polyp. The polyp can be removed using vacuum pressure on the colonoscope or another tool on the end of the scope.When the doctor is finished, he or she sucks the extra air out of your intestine and gently pulls the colonoscope out. The test usually takes 20-90 minutes, depending on whether any polyps are removed.


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