A colonoscopy is a videoscopic investigation of the large intestine or colon.  A colonoscope is used which is a thin, flexible endoscope. It is about as thick as a little finger. It is passed through the anus and into the colon. It can be pushed all the way round the colon as far as the caecum (where the small and large intestine meet). The colonoscope contains fibre optic channels which allow light to be shone into the colon and transmit images back to the video screen. The colonoscope also has a 'side channel' down which devices can be passed. These can be manipulated by the operator. For example, the operator may take small sample (biopsy) from the inside lining of the colon by using an thin 'grabbing' instrument.

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A colonoscopy may be advised if you have symptoms such as bleeding from the anus, pains in the lower abdomen, persistent diarrhoea, or other symptoms thought to be coming from the colon.

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The colon needs to be empty so that the operator can get a clear view. You will be instructed on how to take a special diet for a few days before the test. You will also be given a strong laxatives to take.

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Colonoscopy is usually performed as a day case procedure. You will usually be given a sedative to help you to relax. This is usually given by an injection into a vein in the back of your hand. The sedative can make you drowsy but it does not 'put you to sleep'. It is not a general anaesthetic. You lie on your side on a couch. The operator will gently push the end of the colonoscope into your anus and up into the colon. The examination usually takes about 20-30 minutes. However, you should allow at least two hours for the whole appointment to prepare, give time for the sedative to work, for the colonoscopy itself, and to recover. A colonoscopy does not hurt, but it can be a little uncomfortable, particularly when the colonoscope is first passed into the anus.

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