Colonoscopy
Camera examination of the entire large bowel, via the rectum.
What it means
Colonoscopy examines the full length of the large bowel using a flexible camera passed through the rectum.
It is unusual among tests in being both diagnostic and preventive. Polyps found during the procedure are removed there and then, and since most bowel cancers develop from polyps over years, removing them prevents cancers that would otherwise have formed.
Bowel preparation — a strong laxative regimen the day before — is the part patients find hardest, and it is also the part that determines whether the examination is adequate.
In practice
The report records how far the scope reached (caecal intubation), the bowel preparation quality, and any polyps removed with their size and number.
Findings determine the surveillance interval — when, or whether, a repeat is needed.
Why it matters
Colonoscopy is indicated for a positive bowel screening test, rectal bleeding with a change in bowel habit, unexplained iron deficiency anaemia, and suspected inflammatory bowel disease.
A positive NHS screening test result requires colonoscopy, not reassurance. Most turn out to be polyps or haemorrhoids rather than cancer — but the whole value of the programme lies in going and finding out.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026