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Flexible sigmoidoscopy

Find out what a flexible sigmoidoscopy is, how you have it and what happens after it.

Flexible sigmoidoscopy looks inside the lower part of your large bowel. It is also called bowel scope or flexi sig.

A doctor or specialist nurse uses a thin flexible tube called a colonoscope. This has a small light and camera at one end. The doctor or nurse puts the tube into your back passage and gently moves it up into the lower part of your bowel. They can see the pictures of the inside of your bowel on a TV monitor.

You usually have this test in the endoscopy unit at the hospital. It may take between 5 to 15 minutes. But you should expect to be in the department for up to 2 hours.

Why you might have it

There are a number of reasons you might have a flexible sigmoidoscopy, including:

  • to help find the cause of your bowel symptoms
  • to check a condition that you have been diagnosed with in the past
  • to look for early signs of cancer as part of the bowel cancer screening programme

Before your test

Your bowel needs to be empty for a flexible sigmoidoscopy.   

In preparation for the test:

  • you might need to have a small enema to help you empty your bowel - you might be given it to do at home or have it when you get to hospital
  • you usually can't eat or drink after the enema -  sometimes you can have clear fluids (water, black tea or coffee) before the test
  • instead of an enema, you might need to drink a liquid bowel preparation (laxative) and follow a special diet for a couple of days before the test

You should get written instructions before your test about what you need to do.

If you are taking iron tablets, you need to stop taking them about a week before your appointment. If you normally take drugs that can cause constipation, you might need to stop these up to 7 days before your test. 

Your appointment letter gives you more details about this.

Contact the hospital for advice before your appointment if you are diabetic or taking medicines to thin your blood.

What happens

When you arrive at the hospital you change into a hospital gown. You might also wear paper shorts with an opening at the back. 

You lie on a narrow bed, on your left side, with your knees bent. You don't normally need drugs to make you drowsy (sedation) while you have the test. 

The doctor or specialist nurse gently puts the colonoscope into your back passage and up into the large bowel. This is uncomfortable, but is not usually painful. If you find it too uncomfortable at any stage tell the doctor or nurse and they will stop. 

You might have pain relief using gas and air (Entonox). This is a fast acting pain relief breathed in through a mouth piece. 


The doctor or nurse puts a small amount of gas through the colonoscope into your bowel. The gas expands the bowel so they can see the lining of the bowel clearly. This can make you feel bloated. 

Photographs of your bowel lining are taken. If the doctor or nurse sees any abnormal areas they will take tissue samples (biopsies). If you have any growths in the bowel lining (polyps), they can be removed with a wire loop put down the colonoscope. The samples are sent to the laboratory to be checked by a pathologist. 

A pathologist is an expert who examines and identifies cells.

After the test

You can usually go home after the test. You can eat and drink as usual. 

You might feel bloated and have mild cramping pain after the test. This is due to the gas that goes into the bowel. The discomfort should pass after a couple of hours. Walking around, warm drinks, and peppermint water may help you to pass wind. 

Possible risks

Flexible sigmoidoscopy is a very safe procedure but your nurse will tell you who to contact if you have any problems after your test. Your doctors will make sure the benefits of having a sigmoidoscopy outweigh any possible risks.

After having a biopsy or polyp removed, you might have some bleeding. This is usually a small amount, and stops on its own within a couple of days. Rarely, you might need a blood transfusion or surgery to stop the bleeding. 

Very rarely there is a small tear in the bowel wall. If this happens you need surgery to repair the tear. 

Your nurse will give you instructions about what to look out for and who to contact if you have any problems at home.

Getting your results

You should get your results within 1 or 2 weeks.

Waiting for test results can be a very worrying time. You might have contact details for a specialist nurse and you can contact them for information if you need to. It can help to talk to a close friend or relative about how you feel.

You can also contact the Cancer Research UK nurses on freephone 0808 800 4040 for information and support. The lines are open from 9am to 5pm, Monday to Friday.

Contact the doctor who arranged the test if you haven’t heard anything after a couple of weeks.

More information

We have more information on tests, treatment and support if you have been diagnosed with cancer.

Last reviewed: 
19 Feb 2016
  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser 
    Blackwell, 2015

  • Complications of Gastrointestinal Endoscopy

    BSG Guidelines in Gastroenterology, 2006

Information and help

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