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Colonoscopy is a useful technique, which allows the surgeon to examine the inside of the large intestine (colon). This permits the diagnosis of disease in the colon but the colonoscope can also be used to treat some conditions, such as polyps, which can be removed.

The colonoscope is a flexible telescope, which is passed through the rectum into the bowel. In addition to direct visual inspection, small samples (biopsies) can be removed and sent for microscopic analysis.

Bowel Preparation for a Colonoscopy

In order to examine the colon it needs to be empty. This means that you have to take a powerful laxative prior to the examination. Most patients will receive two doses of a laxative (Fleet). If you are over 75 years old, or have kidney disease you may be given picolax, a different laxative, which is safer in these circumstances.  

The examination is usually in the afternoon so you take the laxatives at 6pm the day before and then 7am on the morning of the examination. After taking the laxatives I would suggest that you do not go to work or leave the house as you will need to get to the lavatory frequently and urgently.  I would continue drink up to about 2 hours before you leave to come to the hospital.  Drinking after that might result in you getting caught short on the way, not good.

Diagram showing stages of a colonoscopy

Diagram showing stages of a colonoscopy


Some vaseline or barrier cream round the anus may also make the area more comfortable. It is essential for the laxatives to work that you drink freely, water or squash. Drinking will help you feel a lot better as it replaces the fluid that you have lost which can be considerable. Some people develop nausea and this happens just drink as well as you can.

On the day before the examination you can have a light breakfast and a very light lunch e.g. fish or chicken and white rice, but you should not eat after that, just have plenty to drink. Its helpful if you avoid very high fibre food such as beans and also food with a lot of pips or seeds.  Similarly, avoid beetroot for a few days prior to the examination as it can look like blood in the bowel and be a bit misleading!  If you feel you need some calories, it is ok to suck boiled sweets as they have no fibre residue. If you take tablets regularly you can take these as usual. You can drink on the morning of the examination and after you have been admitted.  If you are diabetic you will receive specific instructions about you tablets but essentially, once you stop eating, you stop taking tablets that reduce your sugar level.  After the examination, when you have had some food, you restart you medication in the normal way.   It is also important that we stop drugs that increase bleeding risk such as warffarin and clopidogrel.  If you are taking these I should have picked this up in clinic and advised you but if not, do let me know.

The examination itself

You will be admitted to the hospital and be asked to sign a consent form to the procedure if you have not already done so in clinic. There is a very slight risk (1-2:1000 chance – national guideline figures) that the procedure can be complicated by perforation of the colon or bleeding during the procedure. This may result in the need for surgery to the colon. In my practice, no patients have required surgery and I have done over 5000 examinations. You will go up to the endoscopy room and asked to lie on your left side. You will be given some oxygen by mask and then I will give some sedation and a painkiller by injection. This will make you drowsy but you will not be “completely out”.  It also has the side effect of making many people forget the procedure. It can take 10-45 minutes to perform but you will be away from the ward longer than this as after you will spend some time in the recovery area.

Click to start the short video of a colonoscopy


Following the procedure you will be returned to your room on the ward where the effects of the sedative will begin to wear off. I will see you and explain the outcome of the examination. You may not recall all I have said because of the continuing effect of the sedative so it is useful to have a companion who can explain the findings later. The sedative however will affect you judgement so it is essential that your companion drive you home. You may get some abdominal colic as the gas used to inspect the bowel is passed but this will wear off. You should not drive a car or operate machinery for 24 hours. I will get the results of any biopsies sent for pathology and these can be discussed when you are reviewed in clinic, but on occasions clinic review is unnecessary.

Why do I need a colonoscopy?

  • To obtain tissue specimen for biopsy
  • To evaluate unexplained anemia
  • To evaluate unexplained blood from the anus, abdominal pain, change in bowel habit (diarrhoea or constipation), or investigate abnormalities seen on a barium enema or CT scan.
  • To determine the type and extent of inflammatory bowel disease (ulcerative colitis and Crohn’s disease)
  • To follow a previous finding of polyps, colon cancer , or a family history of colon cancer


  • Bowel perforation (hole), requiring a repair operation (1-2 per 1,000 tests)
  • Heavy or persistent bleeding from biopsy or polyp-removal sites (1 out of 1,000 tests)
  • Adverse reaction to sedative medication, causing breathing problems or low blood pressure (4 out of 10,000 tests)
  • Infection requiring antibiotic therapy (very rare)


I have performed over 5000 colonoscopies. I have not had a single perforation requiring surgery. Two patients have bled after a polypectomy and were managed without surgery.  The other main quality indicator is the percentage of examinations where you can see all the bowel to the very end, the caecum. My completion rate is constantly monitored in three monthly intervals by the endoscopy department at Addenbrookes and varies between 92% and 100%.  It should be over 90%.

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