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Colonoscopy & Flexisigmoidoscopy

What is a Colonoscopy?

A colonoscopy is a specialised examination where your doctor guides a colonoscope through the anus to examine the inside of the large bowel. A colonoscope is a long, thin and flexible tube. It is approximately the thickness of the index finger with a video camera attached to one end. The colonoscope is then guided around the large bowel by the doctor so that the bowel lining can be inspected. It is normally performed under sedation and the large bowel will need to be empty and free of faeces. To do this, sachets of a special powder to mix with water will be provided to drink the day before the colonoscopy to clear the large bowel.

A flexible sigmoidoscopy is an examination very similar to a colonoscopy which uses a flexible tube to look at only the left side of the bowel. It has a shorter procedure time and sedation is usually not required.  An enema is given on the day of the flexible sigmoidoscopy to clear the lower part of the large bowel. However, only the left side of the large bowel is seen. Therefore a normal finding only refers to the left side of the large bowel. If polyps are found, a colonoscopy is needed to make sure there are no polyps on the right side of the bowel.

Why is a Colonoscopy performed?

A colonoscopy may be recommended when you have symptoms including, but not limited to, change in bowel habits, unexplained abdominal symptoms, anaemia, and blood in the stool. This allows your doctor to assess for colonic conditions such as inflammation, polyps (small abnormal tissue growths), haemorrhoids (piles), or cancer. During the procedure, air is inflated slowly to help the colonoscope move around the large bowel and to allow the doctor inspect the bowel lining. A small pinch of tissue (biopsy) or polyp may be taken during the procedure. The tissue is removed by using tiny forceps which are passed through the colonoscope and you will not feel any pain while this takes place. If a polyp (small growth on the bowel wall) is found, it can also be removed at the same time. These polyps may bleed or become cancerous over time if not removed.

What are the benefits?

A colonoscopy allows the doctor to diagnose and assess a range of conditions including inflammation, infection, polyps and cancer. It allows the doctor the option of taking biopsies to analyse parts of the large bowel lining which may be abnormal. It enables the doctor to remove polyps without the need (in the vast majority of cases) for an operation.

What are the risks?

Although colonoscopy is a generally safe and commonly performed procedure, complications can sometimes occur. Common (usually temporary) complications include bloating and discomfort due to the air inflated into the colon during the procedure.

Bleeding may occur particularly after biopsy or polyp removal. Although often minor and self-limiting, if persistent it may require blood transfusion or reinsertion of the colonoscope to control the bleeding.

Perforation (tear of the colon) may occur from the procedure. The risk is less than 1 in 1000 cases but may be higher if it is performed to treat larger polyps. If this occurs, it may require hospitalisation, possibly an operation to repair the tear and stoma creation.

It may not always be possible to complete the colonoscopy. This may be due to insufficient bowel cleansing or because you have asked us to stop the procedure. It may also be due to the shape of your large bowel that prevents safe passage of the colonoscope.

If you require sedation there is a small risk that the sedative may affect your breathing. An assessment of the general health will be performed prior to the colonoscopy to reduce this risk and close monitoring will take place during and after the colonoscopy.

As with most investigations, the colonoscopy is not 100% accurate and therefore abnormalities in the large bowel may be missed, including cancers, especially with incomplete bowel cleansing.

Other rare complications include reactions to medications, plasters and latex gloves.  Rarely, heart attack, stroke or death as a result of complications may occur.

What are the alternatives?

Double contrast barium enema is an X-ray of the large bowel taken after a chalky mixture of powdered barium with water and air is introduced through the anus into the large bowel. A bowel cleansing preparation is required to empty the large bowel, similar to the ones used for a colonoscopy. This test almost examines the whole of the large bowel but can miss small polyps. If polyps are found during this test, then a colonoscopy will need to be carried out later to find the polyp and remove it.

Computed Tomography (CT) virtual colonoscopy, also known as CT pneumocolon, is an investigation that involves using a CT scan to create detailed pictures of the large bowel in ‘slice sections’. A small tube will be inserted into your back passage and air will be blown to inflate and stretch the large bowel. CT images of the large bowel will be taken with the patient lying on the back and on the tummy during the scan. Although this test provides detailed images of the large bowel, it can still miss small polyps. A colonoscopy will need to be carried out later if polyps were found on this test.


After the colonoscopy, the patient will be monitored and observed in the recovery area. Patients are advised not to drive or operate machinery on the same day if they have received sedation. Mild problems such as bloating, cramping and discomfort can last up to 24 hours.

Frequently Asked Questions

Will I have diarrhoea when I take my bowel preparation?

You will experience loose motions when you take your bowel preparation and you are advised to stay close to the toilet.

Will I be able to eat before my colonoscopy?

You should not eat or drink anything for approximately 2-4 hours before your colonoscopy, to ensure that your stomach is empty.  You will receive sedation which will make you sleepy and relaxed. However, sometimes people may experience sickness and may even vomit during the procedure. By keeping your stomach empty there is less likelihood of any fluid entering your lungs should you vomit.

If I choose to have sedation, what medications may I receive?

You may be given some Buscopan to relax the bowel during colonoscopy. Sedatives may also be given. Common painkillers may be used during the procedure. Both these treatments can affect your mental ability to think clearly for up to 24 hours after they are given, even though you feel wide awake. For this reason, you will need someone to collect you from the hospital and take you home should you choose to have sedation.

Do I need to have someone with me for the next 24 hours?

You are advised to have someone with you for the next 24 hours. Sedation will not normally be given if no responsible adult is able to collect you and stay with you for 24 hours.

Can I choose to have Entonox (Gas and Air) instead of sedation?

Entonox is a gas that you may be offered to help you manage your pain or discomfort during colonoscopy. It is commonly known as ‘gas and air’ and it is often used during child birth as a short acting painkiller. Entonox can make you feel drowsy and a little light headed. However these sensations disappear rapidly after you stop using Entonox. You do not need an adult to accompany you or stay overnight.

Will I experience much pain and discomfort during colonoscopy?

During the procedure, you may experience some abdominal discomfort due to the bowel being inflated with air. This discomfort should begin to settle once the procedure is finished. We will make sure your discomfort level will be kept to a minimum and we will offer you some painkillers and muscle relaxant should the need arise. Whilst these medications can help you to relax, it will not put you to sleep.

When will I find out the results of the colonoscopy?

You will be given most of your results on the day should you wish to have it. However, the biopsy results will take approximately 14 days. You can get those results either through your GP or during the follow up appointment.