Key points about colonoscopy

  • A colonoscopy is a test used to look at the lining of the bowel (colon or large intestine).
  • A colonoscope is a long, soft flexible tube with a tiny video camera and a light inside.
  • It's gently put inside your bottom and pushed up and around inside your bowel.
  • A colonoscopy might be done to look for causes of tummy pain, bleeding from the bottom, anaemia, ongoing diarrhoea or weight loss.
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Video: Colonoscopy information

A short animation telling you what to expect during your colonoscopy procedure. This video may take a few moments to load.

(Mercy Hospital Dunedin, NZ, 2020)

A colonoscopy might be done:

  • To look for causes of tummy pain, bleeding from the bottom (rectum), anaemia, ongoing diarrhoea (runny poo) or weight loss.
  • If you've had bowel polyps before, you may need a follow-up colonoscopy to look for and remove and further polyps. This is to lower your chance of getting bowel cancer. Bowel polyps are fleshy lumps that grow on the lining inside your bowel.
  • To look for bowel cancer if you've had lots of family/whānau members with bowel cancer – talk to your healthcare provider about this. They can guide you on whether you need a colonoscopy and when, based on family history (eg, number of family members with bowel cancer, their age when they had it and how closely related you are). 
  • If you've been screened through the National Bowel Screening Programme and blood was found in your poo. 

To be able to see the inside of the bowel clearly with the colonoscope, your bowel needs to be completely empty.

In the days leading up to your colonosocopy, you'll be on a special diet. This will be different depending on the clinic you go to but you'll be given detailed instructions. You probably won't be able to eat solid food the day before your test and will only be able to drink water and tea or coffee without milk.

You'll be given a laxative (medicine to make you poo) to help clean out your bowel. This can be pills or liquid and you'll need to follow the instructions carefully. You will have to stay near a toilet as you might poo a lot. It can be uncomfortable and some people find it embarrassing but it is necessary. Ask the clinic staff if you're not sure what to do. Read more about bowel cleansing medicines.

Some of your usual medicines can interfere with the preparation for a colonoscopy. Tell your doctor or nurse what medicines you're taking. You may need to change your dose or stop some medicines for a while. For example it's likely that blood thinners, including aspirin, will need to be stopped.

A colonoscopy is done at a public or private hospital clinic. The test itself takes less than 45 minutes, but you should allow 3 hours for your visit. It's best if you can take someone with you, especially to go home with you afterwards. 

Before the test you'll need to change into a hospital gown. Your doctor or nurse will describe what's going to happen and you'll have a chance to ask questions. You'll discuss whether to have a sedative to help you relax, and you'll have to sign a consent form allowing the test to be done.

When you're ready, you'll be asked to lie on your side or back. A small needle will be put into your hand, and any sedative will be given directly into your blood stream. There'll be a nurse with you to help you and to explain what's happening. The person doing the test will gently insert the colonoscope into your bottom and slowly move it along the inside of your bowel. Air will be pumped in to make things easier to see.

The video camera on the colonoscope sends pictures to a TV screen, allowing the doctor or nurse to see the lining of your bowel. They will examine the lining as they slowly pull out the colonoscope. A colonoscopy isn't usually painful, but you might feel pressure, bloating or cramping during the test. A sedative or painkiller can help you relax and help with any soreness. Sometimes an instrument can be inserted along the colonoscope, and a small sample (a biopsy) or a polyp removed. This doesn't hurt.

Sometimes the doctor or nurse can't pass the colonoscope around the whole bowel. They will let you know whether you need any other tests.

If you've been given a sedative during the test, someone must take you home and stay with you. Even if you feel alert after the test, your judgement and reactions could be affected for the rest of the day. You won't be able to drive for at least 12 hours.

You might feel some cramping or bloating because of the air put into the colon during the examination. This will get better when you fart (pass wind).

You should be able to eat after the test, but you might be advised to eat a special diet and not do vigorous exercise – especially if you've had polyps removed. The doctor or nurse who did your colonoscopy will arrange for any follow-up you need, and for you and your healthcare provider to get a copy of the results. 

Colonoscopy is normally a safe test and complications are unusual. Significant complications occur in only about 1 in a 1000 tests.

There are a few risks to be aware of. These are rare but include:

  • Bleeding if a tissue sample is taken for testing. This usually stops on its own or can be controlled through the colonoscope.
  • An allergic reaction to the sedative.
  • Tearing of the bowel wall (perforation). If this happens you'll need to stay in hospital and could need surgery to fix it. 

The following links provide further information on colonoscopy.

Colonoscopy(external link) Mayo Clinic, US
Tests and investigations(external link) Bowel Cancer NZ
About colonoscopy(external link) Timetoscreen NZ

For information about the most common bowel preparation laxative Gylcoprep C detailed medicines information sheet(external link) Medsafe NZ


Bowel cancer(external link) Ministry of Health, NZ, 2012
Further investigation – colonoscopy results(external link) Health Ed, NZ, 2022

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Credits: Healthify editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Dr Emma Dunning, Clinical Editor and Advisor

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