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Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

A colonoscopy is a procedure using a camera to check the inside of your bowel, with the aim of looking for any signs that are causing your symptoms or as part of a regular colorectal cancer screening.

A colonoscope is a thin, flexible tube, the size of a pen, that is passed into your rectum. It has a camera on the end to view different parts of your bowels and may take some photos for future reference. It's usually done in an outpatient clinic by a gastroenterologist or colorectal surgeon.

In order to get a good view, it's essential your bowel is cleared out beforehand, and they may blow a little gas in to see the bowel lining fully. It just views the rectum and large bowel (the colon), not the small bowel (intestines).

Why do I need a colonoscopy?

Your doctor may have referred you to investigate symptoms, such as a persistent change in bowel habits (diarrhea or constipation), abdominal pain, or bleeding from the rectum. Other reasons for a colonoscopy are unexplained weight loss, reduced appetite or fatigue, and iron deficiency anemia with no obvious cause. Your doctor may have found a lump on examining your abdomen that requires a colonoscopy.

These can represent conditions such as inflammatory bowel disease (either Crohn’s disease or ulcerative colitis), diverticular disease, or bowel cancer.

Recommendations for when to start screening for colorectal cancer vary based on age and family history.

What might the doctor find on a colonoscopy?

Tiny growths called polyps are one possible finding in your bowel – these are usually harmless, but the doctor will take a tissue sample in case they indicate something more serious.

The doctor will look for any abnormalities in the bowel wall that could indicate disease and any changes to the structure that could be causing a blockage. Inflammatory bowel conditions, diverticular disease, and bowel cancer all have distinct appearances on colonoscopy. They will take tissue biopsies of any unusual areas to determine the exact cause and analyze it under a microscope.

It's also common for the doctor not to find anything concerning during the procedure.

How do I prepare for a colonoscopy?

You’ll receive a letter in advance of the procedure to tell you how to prepare. The advice is usually that two days before the colonoscopy, your diet should switch to more bland foods without sauce and spices.

The day before, you’ll be asked to only drink clear liquids and take strong laxatives to clear out your bowels so that they can get a clear view with the camera. It’s best to stay close to the toilet to prevent any unfortunate accidents.

The actual procedure should take around 30 to 45 minutes, but you should allow at least half a day for everything, and you may feel a bit drowsy afterward – someone else should drive you home. You should receive your results after 2 to 3 weeks once any tissue samples have been processed.

Will I be put to sleep for this procedure?

You will typically be put to sleep for the procedure unless there is a specific reason for you not to be given a general anesthetic. To help you relax, you may be offered a sedative medication through a vein or gas and air to breathe in.

Most people tolerate the procedure fairly well, and the doctor carrying out the procedure will be experienced and aim to put you at ease. You might feel a bit self-conscious, as staff will be assisting the doctor during the process, but rest assured that the team is very used to doing this and keeping you comfortable.

Related topics

Read about: Bowel cancer screening

Read about: Bowel cancer

Read about: Cancer

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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