A colonoscope is used to examine the lining of the bowel for abnormalities. This test is called a colonoscopy and is the most effective way to diagnose bowel cancer.

The bowel needs to be completely empty, so you will need to follow a careful diet before the test. You will also need to take a laxative. The department carrying out your colonoscopy will give you information about this.

Before the colonoscopy, you may be given a sedative to help you relax. Once you are lying on your side, a thin, very flexible tube with a camera on the end (colonoscope) is passed gently into your back passage. The doctor or nurse will look inside your bowel and may take photographs and samples of cells to be examined later. Most colonoscopies are problem free, but complications are possible.

It can take up to three weeks before the results of your colonoscopy are ready. This can be an anxious time. Try speaking with a close friend or relative about your thoughts and feelings.

What is a colonoscopy?

Having a colonoscopy

Dr Ana Wilson, Consultant Gastroenterologist, explains what to expect if you're having a colonoscopy.

About our cancer information videos

Having a colonoscopy

Dr Ana Wilson, Consultant Gastroenterologist, explains what to expect if you're having a colonoscopy.

About our cancer information videos

Colonoscopy assessment

You will usually be assessed at your local hospital or screening centre. In some parts of Scotland and Wales, you may be assessed over the phone.

The nurse will explain what your test result means and answer your questions. They will also assess if you are fit to have a colonoscopy. They will explain how a colonoscopy is done, as well as the benefits and risks of having it. The nurse may be called a specialist screening practitioner (SSP).

A colonoscopy isn’t right for everyone. You may be offered a different test if you’re not able to have one. This is usually a virtual colonoscopy (sometimes called a CTC scan or colonogram).

Before a colonoscopy

Your bowel has to be completely empty for a colonoscopy. You will be given instructions on what you can eat and drink the day before the test. The screening centre or hospital will also give you a medicine (laxative) to empty your bowel.

The colonoscopy is usually done in the hospital endoscopy unit and takes about an hour. The test can also see if there are any polyps in your bowel.

Having a colonoscopy

You may be given a sedative just before the test. This helps you feel more relaxed during the colonoscopy.

Some people may be offered entonox (gas and air) instead of a sedative. Entonox is a gas that can help relieve pain. You can breathe in as much as you need through a mouthpiece.

Having a colonoscopy can be uncomfortable, but is not usually painful.

Once you’re lying on your side, the doctor or nurse will gently pass a flexible tube (a colonoscope) into your back passage. There is a tiny light and camera on the end of the colonoscope.

During the test, the camera is used to photograph any areas of the bowel that look abnormal. They may also take samples (biopsies) from these areas. The biopsies will be sent to the laboratory and checked for cancer cells.

If there are polyps, these can usually be removed using a wire loop that is passed down the colonoscope. The doctor or nurse will tell you at the time if they remove any polyps or take biopsies. If they do, you will be contacted within two to three weeks with the results.

I was a bit nervous about the colonoscopy, but it wasn’t bad. They give you a mild sedative which helps and all I felt was a bit of discomfort.


After a colonoscopy

Most people are ready to go home a couple of hours after their test.

If you had a sedative, you’ll need someone to collect you from the hospital. After having a sedative, you should have someone with you for 12 hours and not drive for 24 hours.

If you had entonox (gas and air), you should be able to drive home when the nurses are happy you have recovered. You won’t need someone to stay with you overnight.

It is rare to have serious problems after the test. But if you have severe tummy pain or a high temperature, pass large amounts of blood or are sick (vomit), contact your GP or the NHS out-of-hours service straight away.

Sometimes it’s not possible to see the whole bowel during a colonoscopy. This can happen if the bowel isn’t completely empty or if the colonoscope can’t pass round a bend in the bowel to reach the end. If this happens, you may be asked to have another colonoscopy, or a virtual colonoscopy.

Risks of colonoscopy

Most people who have a colonoscopy have no problems. But, rarely, there can be complications.

About 1 in 250 people have heavy bleeding after having a polyp or tissue sample removed. They may need to go into hospital to have this treated.

There is a small risk of a tear or damage to the lining of the bowel. This happens in about 1 in 1500 people having the test. An operation is nearly always needed to repair the tear.

Very rarely, a person may die as a result of having a colonoscopy. This happens in about 1 in every 10,000 colonoscopies. You will be assessed before you have a colonoscopy to check it is suitable for you. You will be offered a different test if the assessment shows you may be at higher risk of problems.

Colonoscopy results

Getting your results

You should get a letter with the results of your colonoscopy within three weeks. If you have polyps removed or biopsies taken during your test, the letter will say if you need further tests or follow-up. Your GP will also get a letter with your results.

If you feel anxious when waiting for your results, you could talk to a relative or close friend. Or you can talk to one of our cancer support specialists on 0808 808 00 00.

Normal result

This means that no polyps or cancer have been found in your bowel. About half the people who have a colonoscopy after a positive FOB test will get a normal result. It is important to be aware of bowel cancer symptoms in future, even if you have a normal result.

In two years, you’ll be offered bowel cancer screening with the FOB kit again if you’re within the invitation age range.


About 40% of people (around 4 out of 10) who have a colonoscopy after an abnormal FOB test are found to have polyps. If one or more polyps are found, they can usually be removed during the colonoscopy. This can help to prevent bowel cancer developing.

The removed polyps will be looked at in the laboratory. Depending on the results, you may be invited to continue with two-yearly bowel cancer screening. Or you may have another colonoscopy, usually in one or three years’ time.

Polyps may come back after being removed.

Other non-cancerous bowel conditions

About 10% of people (around 1 in 10) may have other changes in their bowel. The most common findings are haemorrhoids (piles) or a bowel condition such as diverticular disease. These conditions may not need treatment if they aren’t causing symptoms. You can ask your GP for information and advice if this test shows you have a bowel condition.


About 10% of people (around 1 in 10) who have a colonoscopy after an abnormal FOB test are diagnosed with bowel cancer. You’ll be referred to a cancer specialist for treatment if a cancer is found.

There is a good chance of curing cancer if it is found at its earliest stage. About 90% (around 9 out of 10) of early-stage bowel cancers can be successfully treated.

If you’re diagnosed with cancer in the colon or rectum, you may find it helpful to read our information about colon cancer or rectal cancer.

Back to Bowel screening

The bowel

The bowel is part of our digestive system and is made up of the small bowel and the large bowel.

The FOB and FIT tests

This test checks bowel motions for tiny amount of ‘hidden blood’. It is not a test for cancer, but can indicate whether further tests are needed to examine the bowel.

Bowel scope screening

This test looks at the lower part of your large bowel. It can help detect cancers at an early stage.