What happens during a colonoscopy?

Written by: Dr Michael Glynn
Edited by: Jay Staniland


A colonoscopy is an endoscopic test, that allows the doctor to see the inner lining of the large intestine. The aim is to visualise the whole of the large bowel and in about half the examinations the lower small bowel (terminal ileum) can also be seen.



What preparation do I need for a colonoscopy?


It is necessary to take a powerful laxative, which is taken at home, before the colonoscopy procedure which causes the bowel to be completely empty. The laxative is usually taken on the day before the procedure.

Sometimes patients find the preparation for a colonoscopy a bit more troublesome than the test itself, as the laxative will require you to use the bathroom often.

The procedure is usually performed under sedation and with some painkiller given immediately beforehand.

An instrument which is used is a thin, flexible tube with a miniature video camera at the end, allowing the doctor to see live images, or take pictures, of the inside of the large intestine.


What is a colonoscopy used for?


Colonoscopy is extremely useful for evaluating symptoms of rectal bleeding and a change in bowel pattern. It helps to detect ulcers, polyps, tumours, inflammation and bleeding.

Problems such as ulcerative colitis, Crohn’s disease and colorectal cancers can be visualised and biopsied. Any polyps that are seen can usually be removed there and then.


Are there any risks of a colonoscopy?


All colonoscopies carry a very small risk of bowel damage (perforation) during the procedure. If a perforation does occur, an operation is often needed to repair it. However the overall risk is very small at about 1:1000. If a polyp is removed this risk may be doubled, but is still small. The colon can also be imaged using a particular CT scan technique, but this does not include the ability to take biopsies or apply therapies.

If you wish to enquire about a Colonoscopy procedure, make an appointment with a specialist gastroenterologist.

By Dr Michael Glynn

Dr Michael Glynn is a highly experienced consultant gastroenterologist/hepatologist based in London, specialising in gastroenterology, hepatology, GI endoscopy and clinical nutrition. His private practice is based at BMI London Independent Hospital. He has held a number of high profile positions within his field, including being National Clinical Director for GI and Liver Diseases within NHS England. Alongside his practice, Dr Glynn is in demand as a medico-legal expert within the fields of general medicine,gastroenterology and hepatology and is dedicated to medical education, serving as Honorary Senior Lecturer at Queen Mary University of London. Dr Glynn has co-edited Hutchinson's Clinical Methods, the oldest continuously published general medical textbook, through a number of editions.

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