Colonoscopy Test
Colonoscopy is a procedure that can check for colon cancer. Learn how it's done and what it can tell the doctor.

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picture of colon test prescription Colonoscopy Test

Why would I need this test?
Colonoscopy (koh-luh-NAH-skuh-pee) is done to detect abnormalities in the colon (large intestine), including early signs of cancer in the colon and rectum. Your doctor may also want you to have a colonoscopy if you have abdominal symptoms (such as pain or discomfort, especially if associated with weight loss or anemia), abnormal results of barium x-ray, chronic diarrhea, constipation, a change in bowel habits, rectal bleeding or anemia.

Through colonoscopy, a doctor can look inside your entire large intestine, from the lowest part - the rectum - all the way up through the colon to the lower end of the small intestine. Inflamed tissue, abnormal growths called polyps (which may be cancerous or non-cancerous), ulcers, bleeding, and muscle spasms can be seen with colonoscopy.

Studies suggest that colonoscopy is a more effective screening method for colon cancer than barium enema.

How can I prepare for this test?
Your colon must be empty for the colonoscopy to be thorough and safe. To prepare you should:

  • Drink only clear liquids and eat no food the day before the procedure.
  • Take a special solution by mouth that flushes the colon clean. You may also need to use suppositories or an enema.
  • Arrange for someone to take you home afterward. You will not be allowed to drive because of the sedatives.

How is this test performed?
Colonoscopy is usually done on an outpatient basis. You are sedated to help prevent any discomfort caused by the procedure. The doctor will insert a long, flexible, lighted tube into your rectum and slowly guide it into your colon. Before advancing the tube, some air is pumped into the colon to keep it open. This helps the doctor to see better. The scope transmits an image of the inside of the colon, so the doctor can carefully examine the lining of the colon.

How long does the procedure take?
Colonoscopy usually takes between 30 to 60 minutes. Make sure you have someone drive you home afterward.

What happens if an abnormality is found?
If anything unusual is in your colon, such as a polyp or inflamed tissue, the doctor can remove a piece of it using tiny instruments passed through the scope. This is called a "biopsy." The tissue is then sent to a laboratory for examination under a microscope. If the exam has identified sites of bleeding in the colon, the doctor can pass a laser, heater probe, or electrical probe, or inject special medicines through the scope and use it to help stop the bleeding.

Are there any risks associated with this test?
Serious risks with colonoscopy are very uncommon. However, excessive bleeding may occur, especially if a large polyp is removed. It is rare, but the lining of the colon can tear.

The laxatives used can sometimes cause an upset in the electrolyte balance or cause damage to the kidneys.

What is a desirable result?
A desirable result is when there are no abnormalities detectable, or a biopsy shows that a polyp is benign (non-cancerous).

By Louis Neipris, MD, Staff Writer
Created on 08/01/2001
Updated on 08/27/2010
  • American College of Gastroenterology. Sedation for your endoscopy.
  • American Cancer Society. Frequently asked questions about colonoscopy and sigmoidoscopy.
  • American Society for Gastrointestinal Endoscopy. Understanding colonoscopy.
  • National Institute of Diabetes and Digestive and Kidney Diseases. Colonoscopy.
Copyright © OptumHealth.
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