Colonoscopy is a test to view the inside of your lower digestive tract (colon and rectum). Sometimes it can show the last part of the small intestine (ileum). During the test, small pieces of tissue may be removed for testing. This is called a biopsy. Small growths, such as polyps, may be removed. 

Doctor and technician performing colonoscopy on patient lying on side.
A camera attached to a flexible tube with a viewing lens is used to take video pictures.

Why is colonoscopy done?

The test is done to:

  • Look for colon cancer

  • Help find the source of belly (abdominal) pain or bleeding

  • Help find the cause of changes in bowel habits

It may be needed every 5 to 10 years (or more often). This depends on factors such as your:

  • Age

  • Health history

  • Family health history

  • Symptoms

  • Results from any past colonoscopy

Risks and possible complications

These include:

  • Bleeding             

  • A hole (puncture) or tear in the colon 

  • Risks of anesthesia

  • A cancer sore (lesion) not being seen or fully removed

Getting ready 

To prepare for the test:

  • Talk with your healthcare provider about the risks of the test (see below). You can also ask about alternatives to the test.

  • Tell your healthcare provider what medicines, vitamins, herbs, and supplements you take. Tell them what health conditions and allergies you have.

  • Make sure your rectum and colon are empty for the test. This is done by following the diet and bowel prep instructions exactly. If you don’t follow the directions, the test may need to be rescheduled.

During the test 

The test is usually done in the hospital on an outpatient basis. Or it's done at an outpatient clinic. Outpatient means you go home the same day. The procedure usually takes about 30 minutes. During that time:

  • You're given relaxing (sedating) medicine through an IV (intravenous) line. You may be drowsy. Or you may be fully asleep.

  • The healthcare provider will first give you a physical exam. This is done to check for anal and rectal problems.

  • Then the anus is lubricated and the scope is inserted.

  • If you're awake, you may feel like you need to have a bowel movement. You may feel pressure as air is pumped into the colon. It’s OK to pass gas during the procedure.

  • Biopsy, polyp removal, or other treatments may be done during the test.

    Outline of abdomen showing scope inserted through anus into entire colon.
    Colonoscopy provides an inside view of the entire colon.

After the test 

You may have gas right after the test. It can help to try to pass it to help prevent later bloating. Your healthcare provider may talk with you about the results right away. Or you may need to schedule a follow-up visit to talk about the results.

After the test, you can go back to your normal eating and other activities. You may be tired from the sedation and need to rest for a few hours. Ask your provider when you can take your regular medicines again.

When to call your healthcare provider

Call your healthcare provider right away if you have any of these:

  • Severe belly (abdominal) pain

  • Fever of 100.4°F (38°C) or higher, or as advised by your provider

  • Rectal bleeding or bloody bowel movements

  • Nausea or vomiting

  • Weakness or dizziness

Online Medical Reviewer: Jen Lehrer MD
Online Medical Reviewer: Raymond Kent Turley BSN MSN RN
Online Medical Reviewer: Rita Sather RN
Date Last Reviewed: 9/1/2021
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