Colonoscopy and Flexible Sigmoidoscopy

Both colonoscopy and flexible sigmoidoscopy use a long narrow flexible camera (colonoscope) to look at the lining of the large bowel (colon).  Sometimes this is referred to as lower gastrointestinal (GI) endoscopy.

A colonoscopy is used to inspect the whole of the colon and sometimes the final part of the small intestine (terminal ileum), whilst a flexible sigmoidoscopy is used to inspect the left side of the colon only.

It aids diagnosis by direct visualisation and allows additional biopsies to be taken, which are often useful for confirming a diagnosis.

It can also be therapeutic so if polyps are found they can also potentially be removed.  This is called polypectomy for smaller polyps, for larger polyps an endomucosal resection (EMR) is required.

Are there any alternative investigations other than colonoscopy?

A colonoscopy is usually the best investigation.  However there are alternatives with advantages and disadvantages of each.

CT pneumocolon (virtual colonoscopy or CTC);

Bowel preparation is used.  Gas is introduced into the bowel via a small pipe placed through the anus.  A CT scan is then performed, usually with you in two different positions.  Images are then produced which radiologists are able to interpret to look for cancers and polyps.  If an abnormality is identified then a colonoscopy is often needed to obtain biopsies, and if polyps are found a colonoscopy is usually needed to remove them.  Small polyps or subtle inflammation of the bowel may be missed.
However sometimes it is not possible to complete a colonoscopy, for reasons such as severe diverticular disease or a very tortuous colon, and in order to fully assess the remaining bowel a CTC is then requested.  The main advantage of a CTC is that other intra-abdominal organs will be seen whereas a colonoscopy only looks at the lining of the colon.  However a CT scan exposes you to ionising radiation which we try to limit if possible.

Minimal Preparation CT enema;

Bowel preparation is not used, but oral contrast is given.  This is usually reserved for more frail patients who are unlikely to tolerate either colonoscopy or CTC.

Preparation for a lower GI endoscopy

Both flexible sigmoidoscopy and colonoscopy are usually performed as a day case procedure and Mr Denzil May can do both of these for you at the Duchy Hospital, Truro, Cornwall.

To enable views during the test it is necessary to completely empty the bowel prior to the procedure. 

You will need to change your diet prior to the test; 

3 days before; avoid foods very high in fibre including pips and seeds, but continue to eat regular meals.

1 days before; eat a normal breakfast in the morning but avoid pips, seeds, porridge, pulses, fruits, nuts, and cereals with high fibre. 

You should stop eating after your breakfast and have clear fluids only the day before your procedure.

Clear fluids include any liquids that are not cloudy. Examples include water, black tea or coffee (no milk), fizzy and soft drinks, cordials and squash (no juice that is red or purple) and clear soups like chicken, beef or vegetable broth (strained without any bits), gelatine (no red or purple), 100% cranberry juice and apple juice.

Strong laxatives will be provided.  Usually Moviprep is used, but on occasion other strong laxatives such as picolax may be given.  This need to be started the day before your procedure.

It is important to follow the instructions, which will be provided for you in writing by the Duchy Hospital.

What to do about medications prior to colonoscopy

If you take iron tablets stop them 1 week prior to your colonoscopy

If you take loperamide (Imodium) or fybogel stop 1 week prior to your colonoscopy.

Blood thinning medication such as clopidogrel, warfarin or one of the novel anticoagulants (rixaroxaban, apixiban, dabigatran) are sometimes stopped.  This will be discussed with you in advance.  If you are not sure please contact my secretary Mrs Liz Venn on 07500 847733.

Continue to take your normal medication otherwise, but make sure it is taken at least one hour before you start the strong laxatives / Moviprep.

What happens during a colonoscopy?

A colonoscopy usually takes about 30-40 minutes, and a flexible sigmoidoscopy 10-20 minutes.

You will be offered intravenous sedation and a painkiller, often fentanyl and midazolam are used.  However this is not always necessary, and sometimes Entonox (laughing gas) is used instead.  Generally sedation is not required for a flexible sigmoidoscopy, but is offered, and for a colonoscopy use of sedation is entirely your choice.

During your procedure you will initially begin on your left hand side.  After a routine safety checklist a rectal examination is performed and the colonoscope is inserted through your anus.  Carbon dioxide or air is used to insufflate your bowel.  This sometimes makes you feel full and bloated.

During the procedure there will likely be periods of time when you experience discomfort.  The bowel responds to stretch and as the scope passes around corners and flexures this can feel uncomfortable.  However the scope is then usually straightened and the discomfort settles.  The scope is usually retroflexed (bent to look back on itself) in both the caecum and the rectum.  This is to avoid missing polyps or lesions on the back of the folds that are not visible looking forward.  Sometimes this feels uncomfortable as the scope is retroflexed. 

Sometimes you will be asked to change position during the procedure, and frequently you will be asked to lie flat on your back.  The nursing staff will help you turn and we will look after the scope during the movement.

Sometimes we apply manual pressure to your abdomen during the test. This is prevent to the scope from “forming a loop” and facilitates completion of the test and reduces discomfort.

If a polyp is found often Mr May will remove this at the time.  A sticky plate will be attached to you, usually your thigh, and the polyp is often lifted away from the bowel wall by injecting fluid underneath then, then using “a snare” with attached diathermy the polyp is removed.  If a large polyp is found, or a lesion suspicious for cancer biopsies will be taken and further scans may be requested.

Complications and risks of a colonoscopy or flexible sigmoidoscopy

Complications following a lower GI endoscopy is rare.  This risks include;

Incomplete examination

It may not be possible to completely examine all of your colon during your colonoscopy.  There are many potential reasons for this including poor bowel preparation & stool limiting views, partial blockage of the bowel by tumour, severe diverticular disease, tortuous colon or previous abdominal surgery (particularly hysterectomy).  An incomplete colonoscopy occurs in about 5% of patients.

Missed pathology

Whilst a colonoscopy is a very accurate test, studies have shown that there is a “polyp miss rate”, even in expert hands.  Most polyps missed are small (less than 1cm) but on occasion larger polyps or cancers are missed.  This is usually when a lesion is sat behind a fold or a flexure, or in an area where the bowel preparation was not optimal.  Approximately 2% of patients with bowel cancer have had a colonoscopy in the 3 years prior to diagnosis.  It is important to appreciate that if symptoms persist following a colonoscopy further tests may be required.


This is a serious and potentially life threatening complication of lower GI endoscopy.  The risk of perforation is small.  For a diagnostic colonoscopy the risk of perforation is about 1 per 1500.  A flexible sigmoidoscopy has a much lower perforation risk of about 1 in every 15,000 procedures.  The risk of perforation is higher if a polyp is removed.

If a perforation of the bowel occurs it almost always needs emergency surgery to repair the perforation.  Occasionally a stoma is necessary.


Bleeding can occur after a polyp is removed or following biopsies.  It occurs in less than 2% of cases.  Occasionally bleeding is significant requiring blood transfusion or further procedures such as a repeat endoscopy, embolization or surgery.

Reaction to drugs (bowel preparation & sedation)

Breathing or heart problems can occur as a reaction to the sedative drugs used during the procedure.  Serious problems are rare and you will be closely monitored throughout your procedure.  Very rarely death occurs as a result of a lower GI endoscopy.  The risk of this is less than 1 in 10,000.

After your colonoscopy or flexible sigmoidoscopy

You will be observed for a short period of time following your test.  Once the effects of the sedation have worn off your will be discharged.  A copy of the endoscopy report with a follow plan will be given to you and Mr May will discuss the findings with you prior to leaving.

If you have had sedation you will need a responsible adult to collect you from hospital and be with you for 24 hours afterwards.

Most people do not have problems following a colonoscopy or flexible sigmoidoscopy.  However contact the hospital if;

  • You continue to bleed from your bottom end
  • You have pain in your tummy that gets worse
  • You develop a fever or feel generally unwell. 

How do I get a referral?

Please use the contact form on this website or contact Mr May’s secretary on 07500 847733.


    Contact Details

    Address: Duchy Hospital, Penventinnie Lane, Truro, Cornwall. TR1 3UP.

    Secretary: Liz Venn

    Tel: 07500 847733

    WhatsApp: 07500 847733


    Duchy Hospital

    Mr Denzil May is the trading name of Kernow Surgeons Ltd

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