Oncologist-approved cancer information from the American Society of Clinical Oncology
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Colonoscopy

Listen to the Cancer.Net Podcast: Colonoscopy–€”What to Expect, adapted from this content.

A colonoscopy is a diagnostic examination used to look inside the entire large intestine, which plays an important role in the body’s ability to process waste. The colon makes up the first five to six feet of the large intestine, and the rectum makes up the last six inches, ending at the anus.

After giving pain medication and a sedative (medication that causes drowsiness) to reduce discomfort, the doctor inserts a colonoscope (a thin, flexible tube with a light and a camera) into the anus and throughout the full length of the colon. The doctor views the image captured by the colonoscope on a video monitor. During the procedure, the doctor can perform a biopsy (the removal of a small amount of tissue for examination under a microscope).

A colonoscopy is used to determine the cause of colorectal problems and to screen for colorectal cancer in people who have no symptoms.

The medical team

Typically, a gastroenterologist performs a colonoscopy with the help of a nurse in a doctor's office or at a hospital. A gastroenterologist is a medical doctor who has completed five to six years of specialized training in gastroenterology, which is the study of the function and diseases of the esophagus, stomach, small intestine, colon and rectum, pancreas, gallbladder, bile ducts, and liver.

Preparing for the procedure

When you schedule the examination, you will get detailed instructions on how to prepare.

Tell your doctor or nurse about all medications you are taking, and ask whether you should take them on the day of the test. In addition, discuss any drug allergies or medical conditions you have.

Because your colon must be empty during the colonoscopy, you will be asked to avoid solid food and drink only clear liquids (such as fat-free bouillon or broth, black coffee, strained fruit juice, or gelatin) for one to three days before the procedure.

In addition to the liquid diet, you will need to take a laxative (a medication that causes bowel movements) or give yourself an enema (a process that involves injecting liquid into your anus to cause bowel movements) the day or night before the colonoscopy. If your doctor prescribes a laxative, it will be given either as a pill or as a powder that you will mix with water before drinking.

Meanwhile, arrange for a friend or family member to drive you home after the procedure because you will be groggy from the sedative. And check your insurance coverage, including whether it covers the medical facility where you will receive the test, the doctor who will perform the colonoscopy, and the anesthesiologist (if an anesthesiologist will be involved in giving the sedation).

Before the procedure, you will be asked to sign a consent form that states you understand the risks and benefits of having the colonoscopy and agree to undergo the test. Talk with your doctor about any concerns you have about the colonoscopy.

During the procedure

When you arrive for your colonoscopy, you will need to remove your clothing and change into a hospital gown. You will then lie on your side on an examining table in a private room with a sheet draped over your body.

The nurse will give you pain medication and a sedative through an intravenous (IV) line, which is inserted in a vein in your arm. You may feel a slight stinging sensation where the IV needle is inserted.

The colonoscope will inflate your colon by blowing air into it to provide a better view of the colorectal lining. As the doctor guides the colonoscope through the curves of your colon, you may need to change your position slightly to allow better access.

If there is an abnormal growth, or polyp, in your colon, the doctor will use a tool at the end of the colonoscope to remove it or perform a biopsy. This usually does not cause pain. Although bleeding may occur at the site where the tissue is removed, the doctor can stop the bleeding using tools passed through the colonoscope.

The procedure typically takes about 30 to 60 minutes to complete.

Generally, the pain medicine and sedative you receive before the colonoscopy should limit the discomfort you may feel during the procedure. However, you may feel cramping. Taking slow, deep breaths may ease this pain. You may also feel discomfort from lying still for an extended time.

In rare cases, the colonoscope may puncture the colon wall, and surgery may be required to repair the perforation (hole). Talk with your doctor if you have any concerns about this small risk.

After the procedure

You will stay at the facility where you have the colonoscopy for up to two hours after the procedure while the effects of the sedative wear off. A friend or family member may then drive you home.

You can expect to resume your normal activities the day after your colonoscopy. However, contact your doctor immediately if you have severe abdominal pain, a fever, bloody bowel movements, dizziness, or weakness.

Questions to ask your doctor

Before your colonoscopy, consider asking your doctor the following questions:

  • Why do you recommend that I have a colonoscopy?
  • Who will perform the colonoscopy?
  • What will happen during the colonoscopy?
  • How long will the procedure take?
  • Will it be painful?
  • Will I receive medications to reduce discomfort?
  • What are the risks and benefits of having a colonoscopy?
  • Whom can I talk to about the costs (if any) of this test I may be responsible for paying?
  • What will happen if I don't have this examination?
  • Will I need to avoid any activities after the colonoscopy?
  • When will I learn the results of the test?
  • Who will explain the results to me?
  • Will I need additional tests?

More Information

Tests and Procedures

Endoscopic Techniques

Cancer Screening

Additional Resources

American College of Gastroenterology: Colonoscopy

National Digestive Diseases Information Clearinghouse: Colonoscopy

MedlinePlus Interactive Tutorial: Colonoscopy

© 2005-2014 American Society of Clinical Oncology (ASCO). All rights reserved worldwide.

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