Having a Colonoscopy

Colonoscopy is a test which allows the doctor to look directly at the lining of the large intestine or colon. The test is performed using a colonoscope, a flexible tube about the thickness of the index finger. Sometimes samples of tissue (biopsies) are taken from the lining of the bowel for laboratory examination. At other times polyps, which are projections of tissue rather like warts, are found and removed during the same procedure. The test itself takes about 20-30 minutes, but may be longer if polyps have to be removed. You can normally be discharged home soon after the procedure.


To allow a clear view the colon must be totally clear of faeces. It is therefore important to follow the advice given about bowel preparation which is given in a separate sheet. If bowel preparation is inadequate the whole procedure may have to be repeated on another occasion. Most medications e.g. for the heart, blood pressure etc. should continue to be taken in the normal way with a small amount of water. Inhalers for asthma should likewise continue to be used. Please let us know if you are on blood-thinning medication e.g. warfarin, aspirin or clopidogrel, or if you are diabetic, especially if on insulin, as special precautions requiring medication and diet may have to be followed. Please check with us or your doctor if you have any queries.


On arrival at the ward you will be met by a nurse. You will have to change into a hospital gown. Your details, blood pressure and pulse will be checked. Let her know about any medication you may be taking or if you are allergic to any medications, plasters etc. If you have any false teeth you will be asked to remove them.

The test may be uncomfortable or painful. Any pain is usually short-lived, as the scope passes round corners, and not too severe. A small needle will usually be inserted into a vein and a sedative and painkiller given before starting the examination. A small device for recording the pulse and breathing will be attached to your finger. This is quite painless. A small sponge attached to a tube will be put inside your nose to give you an increased supply of oxygen.

The colonoscope will then be inserted into your back passage and passed around the large bowel. Air will be introduced into your colon to get a better view. You may feel as though you want to empty your bowel because the colonoscope is felt by the intestine to be a motion. If you should pass wind or motions during the test do not feel embarrassed as the doctors and nurses are quite used to this happening.


CT colography is sometimes used to examine the colon. It is less invasive than colonoscopy but involves the use of radiation. In most situations, colonoscopy is more accurate than X-rays. With CT colography, biopsies cannot be taken nor polyps removed. A flexible sigmoidoscopy is sometimes performed to examine just the lower colon. This is essentially the same examination as colonoscopy, except for the extent of examination.


With sedation, you will probably go to sleep and wake up feeling tired for the remainder of the day. You may feel bloated or have wind pains following the colonoscopy but these will usually pass off over the next few hours. If you have had a biopsy taken or a polyp removed, a small amount of blood may be passed. This need not cause alarm.

Should the amount of blood be excessive or the bleeding continues, or if you develop severe or persistent pain in the abdomen, please contact the Parkside Hospital at 8971 8000. Outside office hours please contact your general practitioner or the Accident & Emergency Department of your local hospital.

Although the doctor will discuss the findings and treatment plan with you after the procedure, you may not remember the conversation, having had sedation, and it is normally best to attend a follow-up clinic appointment for a full discussion. The doctor will however speak to a relative or friend if you wish. You may not drive or cycle for 24 hours afterwards and it is unwise to operate machinery or make important decisions. There is a small risk of excessive sedation which may suppress the breathing and be potentially serious. With any medication there is a small risk of an allergic reaction.


These are uncommon, but include allergy to the drugs used, suppression of breathing due to the sedation, aspiration pneumonia and damage to the intestine by the colonoscope, causing perforation (tear) or bleeding. The latter complications may necessitate surgery. Additionally, although there is a wide range of variability, endoscopic examination can be fairly stressful. As such the effect on the heart and lungs may be comparable to a certain degree of physical exertion. This may be relevant for patients with asthma or bronchitis, or those with heart disease.

Should polyp removal be necessary, the risk of bleeding or perforation will be increased.

Studies have shown that, even when a colonoscopy is performed with a perfectly reasonable standard of care by a skilled endoscopist, some abnormalities can still be missed.


To allow a clear view of your colon, your bowel must be completely clear of faeces. Please follow the following instructions carefully, to help your doctor examine your intestine and, if necessary, remove any polyps under the best circumstances.

  1. Do not take iron tablets, bran, or fibre supplements such as Fybogel or Regulan for 7 days before the test
  2. Avoid fibre-containing foods, i.e. fruit, vegetables and nuts for four days before the test.
  3. For a late afternoon or evening examination, using Picolax:
    • Considerably increase your fluid intake 24 hours before your examination.
    • For 24 hours before the examination, take only fluids eg glucose drinks, bovril, tea or coffee with sugar, and NO SOLIDS.
    • At about 6 pm on the evening before your examination, take one of the doses of Picolax provided. Take the second dose of Picolax around 8 am on the morning of your examination.  If instructed by your Consultant, take the third dose at about 10 am. After each dose of Picolax drink at least one tumbler of clear fluid.
    • For a morning or early afternoon examination, the times have to be adjusted accordingly.
  4. If you are prone to constipation, one or more additional doses of a proprietary purgative may be required, in addition to the above medications, to ensure the colon is adequately cleared. If in doubt, please check with your doctor.
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