Having a Colonoscopy

Having a Colonoscopy

Patient Information

Endoscopy Department

• Author ID: SP/CSL
• Leaflet Ref: End 001
• Version: 13
• Leaflet title: Having a Colonoscopy
• Last review: July 2025
• Expiry Date: July 2027

1. What is a Colonoscopy?

Your doctor has advised that you should have a test to look inside your large bowel (also called the large intestine or the colon).  Sometimes, it is also possible to examine the very end portion of your small bowel (called the terminal ileum) where it joins to the end of the colon.  The medical name of the test is a colonoscopy.  It is usually carried out by an endoscopist, who is a doctor or a specialist nurse.

The instrument used for this test is called a colonoscope.  It is a long flexible tube about the same thickness as your little finger.  A bright light and camera at the end allows the doctor to see the lining of your large bowel on a television screen.

During the test, the endoscopist may need to take some tissue samples (biopsies) from the lining of the large bowel for further analysis. This is completely painless. Photographs may also be taken for your medical records.

2. Why do I need to have a colonoscopy?

You have been advised to have this test to try to find the cause of your symptoms.  This test helps your doctor to decide what treatment you may need and if further tests are needed.

There are many reasons why this test may be recommended, and your doctor will go through this with you.  Common reasons for this test include:

• a change in your usual bowel habit to constipation or diarrhoea
• bleeding from the back passage
• to find the cause of anaemia
• to review a known bowel condition (e.g. inflammatory bowel disease, colonic polyps)
• to assess or treat an abnormality seen on other tests, such as barium enema or CT scan
• a strong family history of bowel cancer
• as part of the National Bowel Cancer Screening Programme

If none of these apply to you, your doctor will explain why you need to have this test.

3. Getting ready for your colonoscopy

Your usual medication

If you are taking any of the medication listed on page 2 of this leaflet and have not been given instructions, please contact the Endoscopy Unit as soon as possible.

Please follow a Low Fibre Diet 3 days before you test:

Foods that are generally allowed on a low fibre diet include:

• White bread without nuts and seeds
• White rice, plain white pasta, and crackers
• Canned or well-cooked vegetables and fruits without skins or seeds
• Fruit and vegetable juice with little or no pulp, flavoured drinks and water
• Tender meat, poultry, fish, eggs and tofu
• Milk and foods made from milk - such as yogurt, pudding, ice cream, cheeses
• Butter, margarine, oils and salad dressings without seeds

You should avoid:

You should avoid:

• Whole-wheat or whole-grain breads, cereals 
• Brown or wild rice and other whole grains, such as oats, kasha, barley, and quinoa
• Dried fruits and prune juice
• Raw fruit, including those with seeds, skin, or membranes, such as berries
• Raw or undercooked vegetables, including sweetcorn
• Dried beans, peas and lentils
• Seeds and nuts and foods containing them, including peanut butter and other nut butters
• Coconut
• Popcorn

Taking Senna tablets 3 days prior to colonoscopy

You have to take Senna tablets 3 days prior to your date for colonoscopy. 

Please take 2 tablets in the evening for 2 consecutive days. 

This is to enhance the quality of the bowel preparation prior to your test. 

You can continue with your normal daily routine for these two days (for example, exercise or work). 

You do not need to take Senna tablets one day before the test. 

When you have started the bowel cleansing preparation, see below.

Taking bowel cleansing preparation 

You will need to take this medicine at home one day before the test. The most common medicines used are: Plenvu®  Moviprep®, Picolax®. 

If you haven’t received your prescription, please contact the hospital pharmacy to arrange for collection. 

Please take the bowel cleansing preparation as per instructions given to you on collection and in the pack. 

If taking Mounjaro for weight loss, please stop taking a week before your procedure, as this delays your stomach emptying If you are taking it for diabetes, please discuss with your diabetic nurse.

It is extremely important that you adhere to the instructions for taking the bowel preparation, so that your bowel is clean before your test. If it is not clean, it may not be possible to see the lining of the bowel adequately during the test.

If you have any questions, please contact the Endoscopy Unit as soon as you can and we will assist you.

On the day of your colonoscopy, you can take small amounts of clear fluids until you arrive for your appointment.

4. What will happen when I arrive?

When you arrive for your colonoscopy, you will be greeted by our reception staff and asked to sit in the waiting room.  Your nurse will ask you to come through to the preparation area shortly before your test. The nurse will need to check your identity and go through any medical conditions, medication and allergies, to ensure it is safe to start the test.  Your oxygen levels, blood pressure and heart rate will be recorded and if you are diabetic, your blood glucose level will also be measured.

The nurse will also check that arrangements have been made for your journey home.  If you are being collected, please ensure that you give us the phone number of the person who will be taking you home (if they are not intending to stay in the department to wait for you).

You will have the opportunity to change into a hospital gown and we can also give you paper shorts, which keep you well covered during the procedure to help keep your dignity.  You may want to bring a pair of full-backed slippers with you.

You will meet your endoscopist before you go through to the Endoscopy Room.  If you have already signed your consent form, they will be happy to answer any questions you may have and confirm the consent. 

A plastic tube, known as a cannula (sometimes called a Venflon® or drip) will be inserted into a vein in your hand or arm.  This allows the sedative drugs to be injected.

5. What happens during the test?

Will I be awake or feel any pain?

The test is not usually painful but can be for some people.  It is usual for most people to be given sedative drugs and a painkiller for colonoscopy.  This is known as intravenous sedation.  Alternatively, you can have Entonox gas during the test.  Some people choose to have a colonoscopy without any drugs at all, but sometimes the test can become too painful.

You will be able to decide which of these options is best for you when you attend for your colonoscopy.

About intravenous sedation

Sedative drugs can be given into a vein in your arm, which will make you drowsy and relaxed.  These drugs will NOT make you go to sleep like a general anaesthetic. You will be able to hear what is said to you and will be able to follow simple instructions during the investigation.  Sometimes the drugs affect your memory, and you may not remember anything about the test afterwards.

You will be connected to a pulse oximeter by a probe placed on your first finger, which measures your oxygen level and heart rate during the procedure. Your blood pressure will also be recorded.

Your comfort level will be monitored during the procedure and sedation can be increased should you experience increased  discomfort during the procedure. 

If you choose to receive sedation, you must arrange for a friend or relative to collect you from the Endoscopy Unit and we recommend that they stay with you afterwards.  You must not drive, ride a bike, operate machinery, climb ladders, sign important documents or work for 24 hours following sedation.  If you are not able to make these arrangements, we will not be able to give you sedation.

About Entonox

Entonox is a colourless gas which does not smell.  The gas is a mixture of oxygen and nitrous oxide.  It is sometimes called laughing gas or “gas and air”.  It is the same gas used by pregnant women during labour.  It can help during colonoscopy because it relieves pain and has a calming effect.

The gas is given by a special mouth-piece which you will be asked to hold during the test.  You will be able to breathe normally through the mouth-piece.  The gas begins to work within 30 seconds, and you may feel slightly lightheaded and sleepy.  You can control the amount of gas that you receive yourself by simply removing the mouth-piece.  Your nurse will monitor you closely throughout the procedure. You can adjust the amount of pain relief you receive by increasing or decreasing the amount of Entonox you inhale during the procedure. 

One of the benefits of Entonox is that once your test is over, the gas quickly leaves the body, and it is usually safe to go home soon after the test.  Unlike with intravenous sedation, you are permitted to drive just 30 minutes after the test if you feel back to your normal self.

Entonox is very safe in most people.  It can make you feel sick, dizzy and give you a dry mouth.  These side effects wear off soon after you stop using the gas.  Entonox may not be suitable for you if you have breathing conditions such as COPD, severe bullous emphysema, or a collapsed lung.

What happens in the procedure room?

You will be shown into the procedure room where the other nurses helping the endoscopist will introduce themselves to you. You will have the opportunity to ask any questions.

You may feel nervous or anxious about the procedure. This is entirely normal. The endoscopist and team will reassure you that this is a regular and safe event. 

The nurse looking after you will then ask you to lie on your left side, ready for the test.

If you are going to have sedation, the nurse will place some tubes under your nose which will provide you with oxygen. We use special probe on your finger to monitor the oxygen levels during the test.  The sedation drugs will be administered into a cannula in your vein, and you will quickly become sleepy and relaxed before the procedure starts.

What happens during the test?

The colonoscope is gently put into your back passage and slowly pushed around your large bowel.  As the colonoscope is pushed past bends in your bowel, you may feel uncomfortable for a short period of time.

Air is blown into the bowel during the test to help the endoscopist do the test.  You may be asked to change position during the test to help pass the colonoscope around your bowel.  The nurses will help you move.

We will ensure that you are well covered up throughout the procedure to preserve your modesty.

Once the colonoscope has been passed around your bowel, the endoscopist will slowly withdraw it to look for anything unusual. Some of the air blown into the bowel will be removed as well, which will make you feel more comfortable.

During the test, samples (biopsies) may be taken from the lining of your bowel for analysis in our laboratory. These will be kept for future tests if they are needed.

What are polyps and what is a polypectomy?

A polyp is a small growth which looks like a wart.  They can grow on the lining of the bowel.  Most polyps are harmless but if they are left to grow, some types of polyps can develop into a cancer.  By removing the polyps, your risk of developing bowel cancer is greatly reduced. Most polyps do not cause any symptoms, but in some cases, they can cause bleeding or a change in bowel habit.

Anyone can get polyps, but certain people are more likely to get them than others.  You may have a greater chance of having polyps if:

• You are 50 years of age or older
• You have had polyps before
• Someone in your family has had polyps or bowel cancer
• You are a smoker, are overweight or have a poor diet

Some polyps are attached to the bowel wall by a stalk, and look like a mushroom, whereas others are flat without a stalk.  Flat polyps are generally a little more difficult to remove.  The removal of a polyp is called a polypectomy and can be achieved by using a variety of instruments through channels in the endoscope.

For most polyps, a snare (wire lasso) is placed around the polyp base and tightened whilst an electric current is passed.  This cuts through the polyp and destroys any blood vessels to prevent bleeding.  Flat or very large polyps can be removed by a technique called EMR (Endoscopic Mucosal Resection).  This involves injecting liquid into the lining of the bowel underneath the polyp.  This raises a cushion of fluid under the polyp, lifting it off the lining of the bowel and allows the wire loop snare to remove the polyp safely. The endoscopist will try to retrieve the polyp tissue once it has been removed, so that it can be analysed under the microscope in the pathology lab.

The time it takes for the procedure to be completed can be variable and depends on the findings encountered. A standard colonoscopy with no large polyp removal would usually take 30 minutes to complete. 

6. What happens after the test?

A nurse will take you to the recovery area where you can rest for as long as you need.

If you received a sedative drug, your oxygen levels, blood pressure and heart rate will be recorded.  It usually takes about 30 minutes for the initial effects of sedation to wear off, but some people may feel fully alert immediately after the test.  The drugs will remain in your blood system for about 24 hours, and you may still feel sleepy or forgetful from time to time.  You will need someone to escort you home and supervise you for this 24-hour period.

Will I be told the results straight away?

Before you leave the department, the nurse or doctor will explain the results of your test.  If you need any treatment or further tests, these will be explained to you.  If biopsies were taken, they will need to be sent to the pathology lab for further analysis. It may take up to two weeks for these results to be available.

You may wish to have a family member or friend with you when you are given the results.

7. What are the risks and side effects to this test?

There are some risks with having this test.  Your doctor will have felt that the benefits of this test outweigh the potential risks before they suggested that you should have it.

Feeling bloated

You may feel bloated (full of wind) and have tummy ache for a few hours after the test because air is blown into the bowel.  You will find this goes away as you pass wind. 

Breathing and blood pressure

If you have sedative drugs, they can cause your breathing to slow down or lower your blood pressure.   This is the reason we do not give high doses of the drugs for this test.  We monitor your breathing and oxygen levels carefully throughout the procedure and this rarely becomes a problem.  We can give a drug (antidote) to reverse the effects of the sedative straight away if needed.

Perforation (tear in the bowel wall)

There is a risk that the colonoscopy can tear (perforate) the bowel wall.  The risk of this is less than 1 for every 1,000 tests done.  A perforation can sometimes settle with intravenous antibiotics and resting your bowel, but an operation is usually required to repair the damage.  If an operation is needed, you may require a stoma (a stoma is an opening into the bowel which empties into a bag on the abdomen) but this is usually temporary.

The risk of perforation is higher if polyps are removed.  The level of risk depends on the size and location of the polyp but can be 1 in 500. If removal of the polyp would be a higher risk procedure, the colonoscopist may decide to simply take samples from it and ask you to return to have the polyp removed at a later date. This will allow you the opportunity to discuss the risks in more detail first.

Bleeding

Bleeding may occur at the site of biopsy or polypectomy.  This usually occurs during the procedure itself but may occur up to 14 days later.  The risk of this is approximately 1 for every 200 to 400 tests done.  Usually the bleeding is minor, and it stops on its own.  Rarely, the bleeding can be more severe and may require a blood transfusion.  Very rarely, a further colonoscopy or even surgery may become necessary to stop the bleeding. 

Missed abnormalities

If the bowel preparation drugs have not worked very well and there is still stool (poo) in your bowel, it can hide abnormalities which can be missed.  Sometimes polyps and even cancers can be difficult to see during the test.

If you are worried about any of these risks, please speak to your doctor or a member of the team before you are due to have this treatment.

8. Are there any alternatives to this procedure?

X-ray tests (a barium enema) and CT scans (a CT virtual colonoscopy) are alternative ways of looking at your large bowel.  The main drawback of these tests is that they only provide pictures of the shape of your bowel and do not allow samples to be taken or polyps to be removed.  They will also expose you to high levels of radiation. You may need similar medicines to clear your bowel for these tests.  Your doctor will have considered a barium enema or CT virtual colonoscopy for you before asking you to have a colonoscopy.

If you do have questions about these alternatives, please mention them to your doctor.