Flexible sigmoidoscopy

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

A specially trained doctor or endoscopist (a healthcare professional trained in endoscopy) uses a thin flexible tube called a colonoscope. This has a small light and camera at one end. They put the tube into your back passage and gently move it up into the lower part of your bowel. This allows them to see the pictures of the inside of your bowel on a TV monitor.

You usually have this test in the endoscopy department in a hospital. It takes up to 15 minutes. But you should expect to be at the hospital for about 2 hours. 

A flexible sigmoidoscopy is different to a colonoscopy. It only looks inside your rectum and the lower part of your bowel, whereas a colonoscopy looks at your entire bowel.

Why you might have it

You might have a flexible sigmoidoscopy to:

  • help find the cause of your bowel symptoms 
  • check a condition that you have been diagnosed with in the past
Diagram showing a sigmoidoscopy

Before your test

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

Your bowel needs to be empty of poo for a flexible sigmoidoscopy. This is so the endoscopist has a clear view of your bowel.  

To prepare you for the test:

  • you may have an enema - you might be sent this to do at home or you may have it when you get to the hospital 
  • instead of an enema, you might be sent a liquid bowel preparation (laxative) to drink and follow a special diet for a couple of days beforehand 
  • you usually can't eat or drink for a few hours before your appointment time

If you're taking iron tablets or drugs that can cause constipation, you need to stop taking them about a week before your appointment. Your appointment letter gives you more details about this. 

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

How you have a flexible sigmoidoscopy

When you arrive at the hospital you're seen by a nurse. They'll check your temperature, blood pressure, breathing and heart rate.

You also see the endoscopist, they'll explain what will happen and ask you to sign a consent form. This is a good time to ask any questions you may have. 

Your nurse will give you a hospital gown to change into. You might also wear paper shorts with an opening at the back. 

During the test

You'll lie on a bed on your left side, with your knees tucked up to your chest. You don't normally need medication to make you relax while you have the test. 

The endoscopist will first check your back passage for any abnormalities. They then gently put the colonoscope into your back passage and up into the large bowel. This is uncomfortable but is not usually painful. They put gel on the colonoscope to make it more comfortable. The gel usually feels cold. 

The doctor or nurse puts a small amount of gas and water through the colonoscope into your bowel. This opens the bowel so they can see the lining of the bowel clearly. This can make you feel bloated and like you want to go to the toilet. Don't worry you won't as your bowel will be empty. You may pass wind during the procedure. Don’t feel embarrassed this is normal for this test. 

If you find it too uncomfortable at any stage tell the endoscopist 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. 

Having a flexible sigmoidoscopy

During the test, they take photographs of your bowel lining. If your 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 remove them with a wire loop. They put the wire loop down the colonoscope. These growths go to the laboratory get checked by a pathologist. 

A pathologist is an expert who looks at and identifies cells.

After the test

You might feel bloated and have mild cramping pain after the test. 

You can eat and drink as usual.

You can usually go home after the test.  

Getting your results

Biopsy results are usually back within 2 weeks. You get your results from your specialist. If your GP referred you for tests, they also get a copy of your results. 

Waiting for biopsy results can be an anxious time. Ask your doctor how long you should expect to wait for your results. 

If you haven't heard anything a couple of weeks after your test, contact your doctor to chase up the results for you. 

For support and information, you can call the Cancer Research UK information nurses on freephone 0808 800 4040, from 9am to 5pm, Monday to Friday. They can give advice about who can help you and what kind of support is available.

What are the 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.

Tear in your bowel

Very rarely there is a small tear in the bowel wall (perforation). If this happens it’s likely you would need surgery to repair the tear. 

  • Localised colon cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.
    G Argilés and others
    Annals of Oncology, 2020. Volume 31, Issue 10 Pages 1291-1305

  • Association of Coloproctology of Great Britain & Ireland (ACPGBI): Guidelines for the management of cancer of the colon, rectum and anus (2017) – diagnosis, investigations and screening
    C Cunnigham and others
    Colorectal disease, 2017. Volume 19, Pages 1-97

  • Gastrointestinal tract (lower) cancers - recognition and referral
    National Institute for Health and Care Excellence (updated February 2021) 

Last reviewed: 
06 Dec 2021
Next review due: 
06 Dec 2024

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