Colonoscopy: preparation and procedure

A colonoscopy is a test that lets the doctor look inside the large intestine (the colon and rectum) using a flexible tube fitted with a small camera, the colonoscope. The doctor views the wall on a screen and can spot abnormalities: inflammation, bleeding, polyps (small growths) or other lesions.

It is a central test in colorectal cancer screening, because it can detect and often remove polyps before they develop further. It is also offered to investigate symptoms such as bleeding, a change in bowel habit or persistent pain.

“How do you prepare for a colonoscopy?” is, by far, the question that comes up most. And for good reason: the preparation is the step that decides whether the test succeeds.

For the doctor to see the colon wall clearly, it must be perfectly clean. The preparation usually has two parts:

• ▪ a low-residue diet in the days before the test (avoiding fruit, vegetables, high-fibre foods and seeds), then clear liquids the day before;
• ▪ a bowel-cleansing solution to drink on a precise schedule, which cleans the colon by producing loose stools.

The exact details — type of product, timings, whether to stop certain medicines such as blood thinners or iron — are given to you by your gastroenterologist. Following the preparation to the letter is essential: incomplete preparation can hide lesions and lead to repeating the test.

A colonoscopy is most often performed under sedation or anaesthesia, after a prior anaesthesia consultation: you are relaxed and generally feel nothing. Lying on your side, you are monitored throughout the test, which usually lasts from a few minutes to about half an hour.

The doctor gently inserts the colonoscope through the anus and moves along the colon, introducing a little air or gas to unfold the wall. If a polyp is spotted, it can often be removed at the same time and sent for analysis. After the test, a period of monitoring is arranged while the sedation wears off.

After sedation or anaesthesia, it is usual not to drive the same day: plan for someone to accompany you home. Bloating or mild discomfort from the air introduced is common and temporary.

The doctor explains what was observed and, if a sample was taken, the analysis results follow after a few days. The instructions for getting back to normal (diet, activities, medication) are given to you by the care team.

A colonoscopy is a common and well-regulated test, but like any procedure it carries risks, generally uncommon: bleeding (especially after removing a polyp), more rarely a perforation of the wall, or a reaction related to the sedation. Your gastroenterologist informs you of these risks and obtains your consent before the test.