Colonoscopy: Preparation, Procedure & Results Explained

Last updated: 18 January 2018

What is a colonoscopy?

A colonoscopy is a fibreoptic ‘telescope’ examination of the colon (large bowel) performed via the rectum.

It gives the operator a direct view of the inside of the colon to detect:

  • Inflammation
  • Polyps
  • Ulcers
  • Tumours
  • Bleeding points

And may allow for therapeutic manoeuvres such as polyp removal.

When would you need a colonoscopy?

Colonoscopy may be performed for:

  • Rectal bleeding
  • Chronic diarrhoea, especially with blood and mucus
  • Weight loss
  • Or a feeling of incomplete evacuation of the bowels, known as tenesmus.

These symptoms may indicate an infection or inflammation of the colon (colitis), or even a tumour of the rectum or sigmoid colon.

Bleeding may also be from a less serious cause such as a polyp, or from dilated fragile blood vessels (angiodysplasia).

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Colonoscopy preparation

In preparation for a colonoscopy, the bowel has to be cleaned out as much as possible.

This starts a few days before the test with a liquid diet, followed by drinking a liquid informally known as ‘bowel prep’, which is available as different brand-names.

This fluid passes straight through without being absorbed, cleaning out the colon along the way.

How is a colonoscopy is performed?

A colonoscopy is usually performed without an anaesthetic. The patient is awake but may be offered a mild sedative to ease anxiety. To enable better visualisation of the bowel, air is often gently pumped into the rectum.

This may cause a sensation of fullness and will always result in some air escaping during and after the procedure as flatus – potentially embarrassing but medical staff are used to it!

If any polyps are seen they may be removed completely during the procedure, or tissue biopsies of polyps or areas of inflammation may be taken for analysis by a pathology laboratory. Polyp removal and tissue biopsy of the bowel are both painless.

The test is usually performed as a day procedure, and patients are allowed home after they have recovered from the effects of the sedative or anaesthetic.

Colonoscopy results explained

Colonoscopy results will usually give a visual description of any abnormalities encountered in the bowel.

If tissue biopsies are taken, the results of these may take a couple of weeks or more.

Related specialists

Related procedures

  • Intravenous cannulation
  • Tissue biopsy

Related tests

Also known as

  • Lower GI endoscopy



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This article is for informational purposes only and should not be taken as medical advice. If in doubt, HealthEngine recommends consulting with a registered health practitioner.

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