Content Map Terms


Test Overview

Colonoscopy is a test that allows your doctor to look at the inner lining of your large intestine (rectum and colon). Your doctor uses a thin, flexible tube called a colonoscope to look at the colon. A colonoscopy helps find ulcers, colon polyps, tumours, and areas of inflammation or bleeding. During the test, tissue samples can be collected (biopsy) and abnormal growths can be taken out. Colonoscopy can also be used as a screening test to check for cancer or precancerous growths in the colon or rectum (polyps).

A colonoscopy looks at the whole colon and the lower part of the small intestine. A test called sigmoidoscopy shows only the rectum and the lower part of the colon.

Before this test, you will need to clean out your colon (colon prep). Colon prep takes 1 to 2 days, depending on which type of prep your doctor recommends. Some preps may be taken the evening before the test. If your doctor ordered a split prep, you'll do part of the prep the evening before and the other part on the day of the test. Plan to stay home during your prep time since you will need to use the toilet often. The colon prep causes loose, frequent stools and diarrhea so that your colon will be empty for the test.

Colonoscopy is one of the many tests that may be used to screen for colon cancer. Other tests include stool tests, sigmoidoscopy, and CT colonography. Which screening test you choose depends on what you prefer. Talk to your doctor about what puts you at risk and what test is best for you.

Why It Is Done

Colonoscopy may be done to:

  • Check for polyps as a screening test for colorectal cancer.
  • Check for the cause of blood in the stool or rectal bleeding.
  • Check for the cause of chronic diarrhea.
  • Check for the cause of iron deficiency anemia.
  • Check the colon after abnormal results from a test, such as a stool test or a CT scan.
  • Watch or treat colon problems like inflammatory bowel disease (IBD).
  • Check for the cause of long-term, unexplained belly or rectal pain.

How To Prepare

Procedures can be stressful. This information will help you understand what you can expect. And it will help you safely prepare for your procedure.

Preparing for the procedure

  • Be sure you have someone to take you home. Anesthesia and pain medicine will make it unsafe for you to drive or get home on your own.
  • Understand exactly what procedure is planned, along with the risks, benefits, and other options.
  • Tell your doctor ALL the medicines and natural health products you take. Some may increase the risk of problems during your procedure. Your doctor will tell you if you should stop taking any of them before the procedure and how soon to do it.
  • If you take aspirin or some other blood thinner, ask your doctor if you should stop taking it before your procedure. Make sure that you understand exactly what your doctor wants you to do. These medicines increase the risk of bleeding.
  • Make sure your doctor and the hospital have a copy of your advance care plan. If you don't have one, you may want to prepare one. It lets others know your health care wishes. It's a good thing to have before any type of surgery or procedure.

Before the procedure

  • Five days before your colonoscopy avoid seeds, nuts, corn, whole grain bread and granola.
  • Follow your doctor's directions about when to stop eating solid foods and drink only clear liquids. You can drink water, clear juices, clear broths, flavoured ice pops, and gelatin (such as Jell-O). Do not eat or drink anything red or purple. This includes grape juice and grape-flavoured ice pops. It also includes fruit punch and cherry gelatin.
  • Drink the "colon prep" liquid as your doctor tells you. You will want to stay home, because the liquid will make you go to the toilet a lot. Your stools will be loose and watery. It's very important to drink all of the liquid. If you have problems drinking it, call your doctor.
  • Do not eat any solid foods after you drink the colon prep.
  • Stop drinking clear liquids for a few hours before the test. Your doctor will tell you how many hours this will be.

How It Is Done

A colonoscopy may be done in a doctor's office, clinic, or a hospital.

During the test, you may get a pain medicine and a sedative put in a vein in your arm (IV). These medicines help you relax and feel sleepy during the test. You may not remember much about the test.

Before the test

You will need to take off most of your clothes. You will be given a gown to wear during the test.

You may lie on your left side with your knees pulled up to your belly. Because you will be given medicine during the colonoscopy, you probably won't remember having the test when you wake up.

Next, the doctor will insert a thin, flexible colonoscope in your anus and move it slowly through the rectum and into your colon. Air will be used to inflate your colon so the doctor can see the lining of the colon on a monitor.

During the test

Your doctor will look at the whole length of your colon as the scope is gently moved in and then out of your colon. You may be asked to change your position during the test.

The doctor may also collect tissue samples (biopsy) or take out growths. Usually, people don't feel anything if a biopsy is done or if polyps are taken out.

The scope is slowly pulled out of your anus, and the air escapes. Your anal area will be cleaned with tissues. If you are having cramps, passing gas may help relieve them.

After the test

After the test, you'll stay at the clinic until you wake up and then have a brief visit from your doctor. Then you'll be allowed to leave with the person who will drive you home.

How long the test takes

The test usually takes 30 to 45 minutes. But it may take longer, depending upon what is found and what is done during the test.

How It Feels

The colon prep will cause diarrhea. Some people also have cramping.

During the test, you may feel very sleepy and relaxed from the sedative and pain medicines. Many people say that they don't remember very much about the test because of the sedative.

You will feel sleepy after the test for a few hours.


There is a small chance for problems from a colonoscopy. The scope may tear the colon or cause bleeding.


If a sample of tissue (biopsy) was collected during the colonoscopy, it will be sent to a lab for tests.

  • Samples of colon tissue are usually sent to a pathology lab, where they are looked at under a microscope for diseases.
  • Other samples of colon tissue may be sent to a microbiology lab to see whether an infection is found.

Your doctor may be able to tell you the results right after the procedure. Other test results are ready in 2 to 4 days. Test results for certain infections may be ready in several weeks.



The lining of the colon looks smooth and pink, with a lot of normal folds. No growths, pouches, bleeding, or inflammation are seen.


Some abnormal findings of colonoscopy include hemorrhoids (the most common cause of blood in the stool), polyps, cancer, one or more sores (ulcers), pouches in the wall of the colon (diverticulosis), and inflammation. A red, swollen lining of the colon (colitis) may be caused by infection or inflammatory bowel disease (IBD).


Adaptation Date: 6/14/2023

Adapted By: HealthLink BC

Adaptation Reviewed By: HealthLink BC