Colonoscopy is a visual examination of the lining of your large bowel (colon) with sedation. A flexible tube (about the thickness of the little finger) is passed through the rectum and around the colon. A small video camera, which can take photos, sends an image onto a video screen. The doctor looks for any abnormalities and if necessary, biopsies (small tissue samples) can be painlessly taken through the colonoscope using tiny forceps. These biopsies are examined under a microscope in the laboratory. Polyps (abnormal growths of tissue) can be removed with biopsy forceps or cold snaring and large polyps are removed using a diathermy snare. This is done by passing a wire loop, like a lasso, over the polyp. The polyp is cut from the bowel lining using electrical current, which seals the tissue and stops bleeding. This current cannot be felt and causes no pain

Why your doctor may suggest a colonoscopy

A colonoscopy may be suggested by your doctor if you have: 

  • Abnormal barium x-ray or abnormal CT Colonography
  •  Bleeding from the bowel 
  •  Abdominal pain 
  • Family history of bowel cancer 
  • Alteration in bowel habit e.g. diarrhoea, constipation
  •  Occult (unseen) blood in the stool 
  • Anaemia
  •  Previous treatment for polyps, bowel cancer or colitis


Your colon must be completely empty of faecal material for the procedure to be thorough and safe. If it is not entirely clean certain areas may be obscured and the test may have to be repeated. Following the preparation, the return from your bowel should resemble urine (pale yellow). This will involve modifications to your diet. You will be given more specific instructions about this including a liquid diet for one to two days and the bowel preparation (laxative). Prior to your procedure it is important for your doctor to know your medical history and in particular any previous endoscopies. Bring a list of your current medication with you, together with any relevant x-rays or barium studies. Fully disclose any health problems you may have had as these may interfere with your colonoscopy, sedation or recovery. 

You should mention: 

  • An allergy or bad reaction to medicines or anaesthetics
  •  Taking medication to thin your blood including Warfarin, Dabigatran, Rivaroxaban, Aspirin or antiplatelet medication: e.g. Clopidogrel or Ticagrelor. Your doctor may ask you to stop taking these medications prior to your procedure or you may be given an alternative dose. 
  • Artificial hip or knee joints. 
  • Prolonged bleeding/clotting disorders or excessive bruising
  •  Diabetes – You must discuss this with your doctor or nurse before undertaking any period of fasting.
  •  Heart and lung problems including artificial heart valves and pacemakers.
  • Cardiac stents in the last 6 months. 
  • If you are pregnant or breast-feeding.

Recommended Bowel Preparations


Risks from a simple examination without any endoscopic therapy are very rare, but can occur after diagnostic therapeutic intervention i.e. removal of polyps. Damage to the wall of the bowel by the instrument can cause a tear or perforation with leakage into the abdomen. This requires hospitalisation, antibiotics and sometimes surgery. (Risk factor: 1 in 1000 procedures) Internal bleeding may occur from the site of the biopsy or polyp removal. It is usually minor and stops on its own. Reaction to the sedation is rare. A polyp or lesion can be missed. The risks of missing polyps/lesions are higher if your bowel is not cleaned properly. If symptoms persist other investigations may be indicated and you are advised to revisit your doctor. If you would like further clarification of these rare complications, please discuss them with your specialist or nurse on admission. 

Please read these points carefully:

You should not drive a car, operate machinery or make any important decisions for 12 hours, as the sedation impairs your reflexes and judgement. Arrange for a friend or relative to take you home.

You must contact your doctor if you suffer severe or prolonged pain or vomiting, passing of blood or high temperature. 

If you have any questions or concerns please raise these with your Doctor or Nurse before the procedure.

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