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A colonoscopy is a procedure that allows your doctor to look at the lining of your large bowel (colon and rectum) for polyps, inflammation or signs of cancer. The procedure may sometimes be carried out by a specialist nurse practitioner, but for simplicity we will refer to ‘doctor’ throughout.

You will meet the doctor carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.

A colonoscopy is a test that allows your doctor to look inside your large bowel. It’s carried out using a long, narrow, flexible, telescopic camera called a colonoscope. Your doctor will pass the colonoscope into your bowel through your anus (back passage).

A colonoscope can help your doctor to find out what is causing symptoms such as:

  • persistent diarrhoea or a change in your bowel habit
  • bleeding from your rectum or blood in your faeces
  • passing slime or mucus from your bowel
  • feeling tired, weak or breathless

These may be the result of:

Sometimes, a colonoscopy is used to confirm the results of other tests, such as a barium enema. You may also be asked to have a colonoscopy if you have had an abnormal faecal occult blood (FOB) test as part of routine bowel cancer screening. If you’re at an increased risk of developing bowel cancer or polyps, you may have a colonoscopy to screen for these conditions even if you have no symptoms. See our frequently asked questions for more information.

During the procedure, your doctor may take a biopsy (sample of tissue) for examination in a laboratory. He or she may also remove any polyps that are growing on your bowel wall. Polyps are usually benign (not cancerous), but they can change into cancer over a number of years. For more information, see our frequently asked questions.

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Image showing where a colonoscope is passed


  • Preparation Preparing for a colonoscopy

    Colonoscopy is carried out in hospital and is usually done as a day case. This means you have the test and go home the same day.

    Your hospital will write to you telling you what you need to do before your colonoscopy. It’s very important that your bowel is completely empty during the test so that your doctor can see it clearly. The main thing that you need to do to prepare for this is to take a strong laxative – these will be provided for you by the hospital. Usually you will need to take them two days before your test but check this in advance with your doctor or nurse.

    The laxative will be quite powerful and will give you diarrhoea, so you will need to stay close to a toilet and drink plenty of clear fluids to make sure you don’t get dehydrated. Clear fluids are those that don’t contain milk such as water, squash and tea and coffee (without milk) – see our frequently asked questions for more information. You may also feel some pain in your abdomen but most people don’t have this. It’s possible that you will find the taste of the laxative unpleasant.

    Other things that you’re likely to be asked to do before your colonoscopy include:

    • stopping taking any iron tablets – these make the inside of your bowel look black and cause constipation, which makes it hard for your doctor to see clearly
    • changing your diet in the two days before your test – this may involve reducing how much fibre you eat

    If you usually take medicines, for example tablets for high blood pressure, take them as usual, unless your doctor tells you not to. He or she may ask you to stop taking some of your usual medicines if they are likely to make you constipated. If you take medicines that affect the way your blood clots, such as warfarin, aspirin or clopidogrel, tell the outpatient department staff when you receive your appointment letter. The staff will tell you whether you need to stop these before the test.

    If you have diabetes and you’re taking insulin or medicines to treat it, contact the outpatient department to tell them. They may be able to arrange for you to be the first to have your colonoscopy on the day of your appointment. You will be given specific information about when to take your medicines or insulin and what to eat before the procedure.

    Your doctor will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to understand what will happen, and you can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead, which you may be asked to do by signing a consent form.

    Bupa Health Assessment: Colon health

    If you are concerned about colon issues, Bupa can help you get a diagnosis.

  • Alternatives What are the alternatives to a colonoscopy?

    A colonoscopy is usually the best investigation for showing the inside of your bowel. However, it isn’t appropriate for everyone. If you can’t have a colonoscopy, your doctor may suggest other tests. The main alternatives are listed below. 

    • Barium enema. A fluid containing barium (a substance which shows up on X-rays) is put into your bowel via your anus. X-ray images of your abdomen (tummy) are taken which show the inside of your bowel.
    • Virtual colonoscopy. This test involves having a CT scan of your abdomen after gas has been pumped into your colon to expand it. A CT scan uses X-rays to produce three-dimensional images of your large bowel and rectum.
    • Flexible sigmoidoscopy. This is a similar procedure to a colonoscopy but it uses a shorter instrument to look inside your rectum and the lower part of your large bowel.
  • The procedure What happens during a colonoscopy?

    The procedure usually takes 30 to 45 minutes to complete.

    Your nurse will ask you to put on a hospital gown that opens at the back or a gown and trousers that have a hole cut in the back.

    You will be asked to wear an oxygen mask or have small tubes placed just under your nostrils through which oxygen is passed. You will have a drip inserted into a vein in the back of your hand to give you any medicines you may need. You will probably be given a sedative and a painkiller to make sure you're relaxed and comfortable during the procedure.

    Your doctor will ask you to lie on your left-hand side and he or she will gently insert the colonoscope into your rectum. Lubricating jelly will be used to make this as easy as possible.

    Air will be pumped into your bowel to make it expand slightly, which makes the colonoscope pass through more easily. This might feel uncomfortable and you may pass some wind. Your doctor will gently move the colonoscope up through your bowel. The colonoscope is flexible and the doctor can rotate the tip of the instrument so that it follows the curves in your bowel.

    The images from the camera at the end of the colonoscope appear on a monitor – these enable your doctor to look at the inside of your bowel. During the procedure you may be asked to change your position – for example turning from your side on to your back. This helps your doctor to look at different areas of your bowel. He or she may press on your abdomen to help move the colonoscope in the right direction.

    During the procedure your doctor may take a biopsy or remove small polyps. This is quick and painless and is done by passing instruments inside the colonoscope. The samples will be sent to a laboratory for testing to see if the cells are benign or malignant (cancerous).

    Image showing where a colonoscope is passed

  • Worried about your colon health?

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  • Aftercare What to expect afterwards

    You will need to rest until the effects of the sedative have passed. You will usually be able to go home when you feel ready but you will need to arrange for someone to drive you home as you’re likely to still feel drowsy after the sedative. Try to have a friend or relative stay with you for the first 12 hours after your colonoscopy.

    At the hospital after your colonoscopy, your doctor may discuss other findings from the test with you before you leave, or you may be given a date for a follow-up appointment. If you have had a biopsy or had polyps removed, your results will be sent to the doctor who referred you for the colonoscopy.

  • Recovery Recovering from a colonoscopy

    If you need pain relief, you can take over-the-counter medicines, such as paracetamol or ibuprofen. Always read the patient information that comes with your medicine and if you have any questions, ask your pharmacist for advice.

    Sedation temporarily affects your co-ordination and reasoning skills, so you must not drive, drink alcohol, operate machinery or sign legal documents for 24 hours afterwards. If you’re in any doubt about driving, contact your motor insurer so that you’re aware of their recommendations, and always follow your doctor’s advice.

    Most people have no problems after a colonoscopy, but you should contact your GP or the hospital department if you:

    • have heavy bleeding from your back passage
    • have a swollen abdomen and abdominal pain that gets worse
    • develop breathlessness or shoulder pain
    • feel unwell and develop a fever (high temperature)
  • Risks What are the risks?

    As with every procedure, there are some risks associated with colonoscopy. We have not included the chance of these happening as they are specific to you and differ for every person. Ask your doctor to explain how these risks apply to you.


    These are the unwanted but mostly temporary effects you may get after having the procedure.

    After having a colonoscopy, you may feel bloated and uncomfortable for a few hours as a result of trapped wind. You may find that lying on your front can help. You may also bleed a little from your back passage, especially if you have had a biopsy or polyp removed.


    Complications are when problems occur during or after the procedure. The main ones related to colonoscopy are listed below.

    • Your doctor may not be able to see all of your bowel. This can happen if your bowel isn’t empty or the colonoscope can’t be passed round a curve. If this happens, you may need to have the colonoscopy done again or have other tests.
    • You may have a reaction to the sedation, which can affect your breathing or your heart. You will be monitored throughout the procedure and treated quickly if this develops.
    • The colonoscope and the other instruments used during the procedure may damage or tear your bowel. If this happens, you may need an operation to repair it.
    • You may have heavy bleeding if you have had biopsies or polyps removed.
  • FAQs FAQs

    What are polyps and why do they have to be removed?


    Polyps are growths inside your bowel. They are quite common and usually don’t cause any problems. However, certain types of polyps can grow into cancers over time so if your doctor finds any polyps during your colonoscopy, he or she will probably remove them.


    Polyps are small, fleshy lumps, usually less than 1cm in size, although they can be bigger. About twenty-five in every 100 people develops a polyp in their lifetime, most often after the age of 60. Men are slightly more likely to develop polyps than women.

    Some polyps are attached to the side of your bowel on a stalk and look a bit like a mushroom, whereas others are flatter and have no stalk. You may have just one polyp, or several.

    Most polyps never cause any problems. However, there is a small chance that over time a type of polyp known as an adenoma will grow into a cancer. It’s now thought that bowel cancer starts as a polyp so if your doctor finds any during your colonoscopy, he or she will probably remove them.

    Some people develop a certain type of polyp that can multiply over time. For this reason, you may be asked to have regular colonoscopies. How often you have these will depend on how many polyps you have had and when a polyp was last found.

    What should I eat and drink before a colonoscopy?


    Your doctor will usually ask you to eat low-fibre foods in the two days before your colonoscopy. The day before the procedure you will need to only drink clear liquids. This is to make sure your bowel is empty so that your doctor can see it clearly during the test.


    A colonoscopy is a test that allows your doctor to look inside your large bowel. In order for your doctor to see it clearly, it needs to be completely empty. To do this you will probably be asked to change what you eat and drink in the two days before the procedure.

    Your doctor will ask you not to eat any high-fibre foods for two days before your colonoscopy. High-fibre foods include most fruit and vegetables, wholemeal bread and pasta, brown rice, pulses and nuts. Instead you will need to stick to low-fibre foods such as lean meat, fish, boiled potatoes without the skin and white bread, pasta and rice. You will also be asked to drink clear fluids only. This means fluids that don’t contain milk such as water, squash, clear soup, meat extract drinks, strained fruit juice, lemonade, jelly (not containing fruit) and tea and coffee (without milk).

    The day before your colonoscopy you will need to stop eating solid foods and have only clear fluids.

    You will receive full instructions before your colonoscopy appointment, which you should follow carefully.

    Will I need to have a colonoscopy as part of screening for bowel cancer?


    Bowel cancer screening aims to find cancer when it’s in the early stages. If blood is found in your faeces (stool) during the first stage of screening, you may be offered a colonoscopy to look at the inside of your bowel.


    Bowel cancer screening aims to find bowel cancer when it’s in the early stages and treatment is more likely to be effective. Screening is offered to all men and women between the ages of 60 and 69 in England and Northern Ireland. In Scotland it’s offered to people aged 50 to 74 and in Wales to anyone aged between 60 and 74. If you’re eligible for screening, you will be offered a test every two years.

    Everyone is offered a test called faecal occult blood (FOB) testing. The test checks for blood in your faeces, which is one of the possible signs of bowel cancer. You will be sent a testing kit and instructions that show you how to take a sample of your faeces. You send this to a laboratory and should usually get the results back within two weeks.

    Out of every 100 people who do the test, about 98 have a normal result. If you have an unclear or abnormal result, it probably means that blood has been found in your faeces. You will be offered more tests to find out what is causing this. One of the tests you may have is a colonoscopy. It’s important to remember that any blood in your faeces may be caused by conditions other than cancer.

    If you would like more information about bowel cancer screening, or are worried about your test results, talk to your GP or nurse.

  • Resources Resources

    Further information


    • Bowel cancer symptoms. Beating Bowel Cancer., published November 2012
    • Ulcerative colitis. Core., published February 2011
    • Crohn’s disease. Core., published February 2011
    • Bowel cancer screening – the colonoscopy investigation. NHS Cancer Screening Programmes., published May 2006
    • Colonoscopy. Macmillan Cancer Support., published August 2010
    • Colorectal cancer. BMJ Best Practice., published February 2013
    • Bowel cancer. British Society of Gastroenterology., accessed 21 December 2012
    • CT colonography. Macmillan Cancer Support., published August 2010
    • Tests and investigations. Beating Bowel Cancer., published December 2012
    • Bowel screening., published October 2012
    • Bowel cancer tests. Cancer Research UK., published October 2011
    • Colonoscopy patient information. Health and Social Care., published May 2010
    • About bowel screening. NHS Bowel Cancer Screening Programme., accessed 30 December 2012
    • Bowel screening. Scottish Bowel Screening Programme., accessed 30 December 2012
    • Bowel cancer. NI Direct., accessed 30 December 2012
    • Bowel Screening Wales., published December 2012
    • Polyps in the bowel. Core., published February 2011
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