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What does a colonoscopy procedure involve?

A colonoscopy looks at the whole of the inside of the large bowel. A flexible tube, called a colonoscope, is used that has a small light and camera at one end. Your consultant puts the tube into your back passage and passes it along the bowel. They can see pictures of the inside of your bowel on a TV monitor. 

You may have a colonoscopy to:

  • help find the cause of your bowel symptoms
  • look for early signs of bowel cancer as part of the national screening programme, or if you are at high risk of bowel cancer
  • monitor you after treatment for bowel cancer

Before your colonoscopy test

You need to have an empty bowel for the test so that we can clearly see the inside of your bowel. You may need to take medications (laxatives) to empty your bowel the day before your test.

Your consultant might ask you to eat a low fibre diet for one or two days before the test. It is very important to drink plenty of clear fluids. This includes:

  • water
  • black tea or coffee
  • squash (not with red or purple colouring)
  • clear soup

After taking the laxatives you might need the toilet often and very suddenly. You may have some cramps. It is sensible to stay at home for a few hours after taking laxatives so that you are near a toilet.

If you take iron tablets or other medicines that can make you constipated, you might need to stop these for 1 week before the test.

What happens during your colonoscopy

You usually have a colonoscopy as an outpatient in the endoscopy department at the hospital. You wear a hospital gown and might also wear paper shorts with an opening at the back.

You are offered medicine to make you drowsy (sedation) and painkillers. You have these as injections into a small tube (cannula) in your vein. Some hospitals use gas and air (Entonox). This is a fast acting pain relief breathed in through a mouth piece.

Lying on your left side, you draw your knees up towards your chest. The colonoscope goes into your back passage (rectum) and passes into your bowel. The tube bends easily so it can pass around the curves in your bowel. The colonoscopist puts a small bit of gas into your bowel. This makes it easier to see all of the bowel lining.

Photographs of the bowel lining are taken. The doctor or nurse can remove tissue samples (biopsies). If they see any growths (polyps) they remove them with a small wire loop put down the colonoscope. You might also have a dye sprayed onto the lining of the bowel to show up any abnormal areas. This is called chromoscopy.

Colonoscopies can be uncomfortable but shouldn’t be painful.