Colonoscopy: the least glamorous medical procedure that could save your life

A colonoscopy uses a long, thin, flexible camera, passed through the back passage (the rectum, for US readers), to look directly at the lining of the bowel. It lets your care team spot problems such as inflammation, polyps and cancer.

Usually your doctor will suggest a colonoscopy if you have signs or test results that might point to a problem in the lower part of your gut. These include:

• Unexplained weight loss
• Changes in bowel habit
• Bleeding from the back passage
• Test results suggesting blood in your stool, such as the FIT (faecal immunochemical test) used in UK bowel cancer screening
• Keeping an eye on a known condition

For a colonoscopy to succeed, the bowel needs to be mostly empty so that any changes can be seen. This involves a 'low residue' (low fibre) diet and strong laxatives known as 'bowel preparation' before the day. The preparation is not a pleasant part of the process and it can be challenging, but it is very important. Good preparation allows a more complete look and reduces the chance of anything being missed.

When you arrive, the nursing team will check you in and make sure you are well and properly prepared before things begin.

A colonoscopy can be uncomfortable. The bowel hangs on a sheet of connective tissue called the mesentery, and it is tension on the mesentery, as the camera moves around, that causes most of the discomfort. There are several options for staying comfortable:

• Nothing: some people have no painkillers or sedation at all
• Gas and air (Entonox): a mix of oxygen and nitrous oxide, breathed through a mouthpiece, that takes the edge off
• Sedation through a vein: a strong painkiller plus something to make you relaxed and sleepy
• Deeper sedation: reserved for particular situations in the UK rather than offered routinely, and used more often in some other countries

You usually start by lying on your side. The endoscopist applies some lubricant jelly and guides the camera in, and might ask you to change position as they move around different parts of the bowel. Often you can watch on a screen, so you see what they see. They use a mix of gas and water to gently open the bowel as they go.

Usually the goal is to travel all the way around the large intestine to the caecum, where the small and large bowel meet, and often a little further into the last part of the small intestine, called the terminal ileum. It is on the way back out that the endoscopist looks most closely at the lining, checking everything is as it should be.

You will be looked after while any sedation wears off. If you were sedated you will need a responsible adult to take you home and stay with you, and you should not drive, drink alcohol or sign anything legally binding for 24 hours. Feeling bloated or crampy for a few hours is common as the gas passes.

Try not to worry if a colonoscopy has been recommended for you. It is a straightforward test and your team will take good care of you before, during and after. And it earns its keep: it can remove polyps before they ever become cancer, or catch a problem at an early stage, when it is easiest to deal with.