Colonoscopy and Preparing for It

What is a colonoscopy?

Colonoscopy is the examination of the inner surface of the large bowel with a thin, flexible instrument carrying a camera, called a colonoscope.

A colonoscopy can assess the whole of the large bowel and, where needed, the last part of the small bowel.

If it is thought necessary during the examination, biopsies can be taken, polyps can be removed and some kinds of bleeding can be treated.

A colonoscopy can be done under sedation or anaesthesia, or without sedation. Which is suitable for you is decided according to your state of health and the practice of the centre where the examination is done.

The information on this page is for general guidance. The instructions on medicines, timing and fasting given to you by the healthcare organisation carrying out your procedure always take precedence.

Why is a colonoscopy done?

A colonoscopy may be done for many reasons, among them:

• Screening for bowel cancer,
• Looking for and removing polyps,
• Blood seen in the stool,
• A positive faecal occult blood test,
• Anaemia of unexplained cause,
• Long-standing diarrhoea or constipation,
• An unexplained change in bowel habit,
• Abdominal pain of unexplained cause,
• Unexplained weight loss,
• The diagnosis and follow-up of inflammatory bowel disease,
• Follow-up of people in whom a polyp has previously been found.

Why does bowel cleansing matter?

For a colonoscopy to succeed, the large bowel must be well cleared of stool.

If stool remains in the bowel, the doctor may not be able to see the whole of the bowel wall well enough. Small polyps or other important findings may be missed.

If the bowel cleansing is very inadequate the colonoscopy may not be completed, and the examination may have to be repeated on another day.

Good bowel preparation is therefore one of the most important conditions for a good-quality colonoscopy.

How should I prepare for a colonoscopy?

The day before the procedure

Take the bowel preparation medicine prescribed to you at the doses and times set out in the written plan given to you by the healthcare organisation carrying out your procedure.

In many preparation programmes the medicine is divided into two doses, with the second taken on the day of the procedure. A different plan may be used in some situations. Do not bring the programme you have been given forward, delay it or change it on your own initiative.

You may need to drink plenty of clear fluids during the preparation. Follow the quantity of fluid and the method of use stated for the medicine you have been given.

As the preparation progresses you will open your bowels more often, and in the end the fluid coming from the bowel is expected to become pale yellow or clear, with no solid stool in it.

Eating

On the day before the procedure, low-residue foods that leave nothing behind in the bowel should be chosen.

Vegetables, salad, fruit, nuts, foods with seeds, wholemeal products, bulgur and foods high in fibre should be avoided.

No solid food should be taken after the time your doctor has told you, and clear fluids should be taken instead.

The day of the procedure

On the day, follow the fasting and clear fluid instructions the healthcare organisation has given you.

If your preparation programme includes a dose to be taken on the day of the procedure, complete it only at the time you have been told. Do not take an extra dose that is not part of your programme.

Patients with high blood pressure

Unless your anaesthetist tells you otherwise, you may take the blood pressure medicine you take regularly with a very small amount of water in the morning.

Follow the advice of your doctor or the anaesthetic team as to whether you should take your other medicines on the morning of the procedure.

Do not drink an unnecessary amount of water or other fluid on the day of the procedure.

Consent form

The clinic’s consent form will be signed.

How is a colonoscopy done?

In the procedure room the patient is generally laid on their left side.

A drip is placed and anaesthesia or sedation is given. Once the patient is asleep the colonoscope is passed gently through the back passage.

Through the camera at the tip of the instrument, the doctor examines the inner surface of the large bowel in high definition on a screen.

If it is thought necessary, a biopsy can be taken or a polyp removed during the same procedure.

Before the procedure the process and the individual benefits and risks are explained, and your informed consent is obtained.

A colonoscopy is mostly completed within 20 to 30 minutes. But the time can vary according to the shape of the bowel and any additional procedures carried out.

After the procedure

Once the procedure is finished the patient is observed in the recovery area.

For a short time there may be:

• Wind,
• Bloating,
• Mild abdominal pain or cramp.

These generally settle quickly.

If sedation or anaesthesia has been given, do not drive a car or ride a bicycle, operate machinery, drink alcohol or make important decisions for 24 hours. Follow the discharge instructions you are given.

Someone should accompany you when you leave the hospital, and if possible you should not be alone for the first 24 hours.

What are the possible risks of a colonoscopy?

Colonoscopy is generally a safe procedure. Even so, as with every medical intervention, there are some risks.

Uncommonly, there may be:

• Bleeding after a biopsy or the removal of a polyp,
• A hole in the wall of the bowel (perforation),
• Infection,
• Breathing and heart problems related to sedation or anaesthesia.

The level of risk can vary with age, accompanying illnesses, the medicines being taken, and whether additional interventions such as a biopsy or the removal of a polyp are carried out during the procedure. Discuss your own risks with the doctor who will carry out the procedure.

When is emergency help needed after the procedure?

If any of the following develops, contact the centre that carried out the procedure at once, or go to the nearest emergency department:

• Severe abdominal pain that does not pass or that increases, or marked swelling of the abdomen,
• Heavy or increasing bleeding from the back passage, or blood clots,
• Fever or shivering,
• Vomiting that does not stop,
• Shortness of breath,
• Dizziness, fainting or marked weakness.

A small amount of blood may be seen after a biopsy or the removal of a polyp; but if the amount of bleeding is increasing, do not wait. If you feel seriously unwell, call the emergency services.

Important

Bowel preparation may not be the same for every patient.

If any of the following applies to you, be sure to tell your doctor when you make your colonoscopy appointment:

• Severe or long-standing constipation
• Kidney failure or chronic kidney disease
• Diabetes
• Heart disease or heart failure
• A pacemaker
• A stent in the coronary arteries
• Taking blood-thinning medicines
• Bowel preparation having been inadequate at a previous colonoscopy
• Taking a large number of regular medicines

In these patients the bowel preparation may need to be started earlier, the medicine used may need to be changed, or some medicines may need to be temporarily rearranged.

For this reason, please read carefully the preparation advice for the particular situations below.

Colonoscopy preparation in patients with severe constipation

In people who have had constipation for a long time, clearing the bowels sufficiently for a colonoscopy can be harder than in other patients.

In particular, people who:

• Open their bowels once or twice a week or less often,
• Use a laxative constantly in order to open their bowels,
• Have had serious constipation for many years,
• Have had inadequate bowel preparation at a previous colonoscopy

must tell their doctor about it when they make the appointment.

Starting the preparation earlier in constipation

In patients with severe constipation, leaving the preparation to the day before the colonoscopy alone may not be enough.

Your doctor may therefore advise you, according to the state of your bowels, to begin the preparation a few days before the colonoscopy.

Three days before the procedure, in constipation

Foods that leave a lot of residue in the bowel should be reduced.

During this period it is appropriate to avoid the following:

• Vegetables and salads
• Fruit with skins and seeds
• Nuts and seeds
• Wholemeal and wholegrain breads
• Bulgur
• Dried pulses
• Sweetcorn
• Fibrous, high-residue foods

Foods that leave less residue in the bowel should be chosen instead.

White bread, rice, pasta, eggs, yoghurt and clear or strained soups may be taken, for example.

Two days before the procedure, in constipation

The low-residue diet continues.

Taking enough fluid is important. But patients on a fluid restriction because of heart or kidney failure should not increase the amount of fluid on their own initiative.

If your doctor thinks it necessary, they may adjust your existing treatment for constipation during this period, or advise an additional medicine to help clear the bowel.

Do not use extra laxatives, enemas or additional doses of the bowel preparation medicine unless your doctor advises it.

One day before the procedure, in constipation

Take the bowel preparation medicine prescribed to you according to the dose and timing plan given to you by the healthcare organisation carrying out the procedure.

Because the standard programme may not be enough in severe constipation, when the preparation starts, whether additional treatment is needed and when the last dose is taken may all be set individually. Do not depart from the written plan.

At the end of the preparation, the fluid passed is expected to contain no solid stool and to have become pale yellow or clear.

The morning of the procedure, in constipation

Follow the fasting, clear fluid and medicine instructions you have been given.

If your preparation programme includes a dose to be taken on the morning of the procedure, take it only at the time you have been told.

Unless the anaesthetist says otherwise, patients with high blood pressure may take the blood pressure medicines they have been told to take with a very small amount of water.

Important warnings in constipation

If you open your bowels only once a week, be sure to tell your doctor.

Because standard preparation may be inadequate in patients with constipation at this level, your preparation programme may be arranged individually by your doctor.

If you have had a colonoscopy before and were told that your bowel cleansing was inadequate, be sure to mention that too.

Good bowel cleansing matters a great deal, so that small polyps and other important lesions are not missed and the colonoscopy does not have to be repeated.

Colonoscopy preparation in patients with kidney failure

If you have kidney disease, bowel cleansing before a colonoscopy must be planned specially.

Bowel cleansing medicines can cause a considerable loss of fluid through diarrhoea. Some preparations can also change the levels of minerals in the blood such as sodium, potassium, magnesium and phosphorus.

These changes, which generally cause no trouble in healthy people, can become important in people whose kidney function is reduced.

What to mention when making an appointment, in kidney disease

Tell your doctor beforehand if any of the following applies:

• You have chronic kidney disease,
• You have been told that your kidney function is low,
• You are having dialysis treatment,
• You have a single kidney and there is a reduction in your kidney function,
• You have previously been treated in hospital for kidney failure,
• Your fluid intake has been restricted by a doctor.

Where it is thought necessary, creatinine, eGFR and electrolytes may be checked before the colonoscopy.

Choosing the bowel cleansing medicine in kidney disease

In patients with kidney disease the bowel cleansing medicine must be chosen by a doctor.

In patients whose kidney function is reduced, PEG (polyethylene glycol) based bowel cleansing solutions are generally preferred.

By contrast, bowel cleansing products containing sodium phosphate should not be used in patients with kidney failure, since they can cause kidney damage and serious mineral disturbances.

Because magnesium is excreted by the kidneys, some bowel cleansing preparations containing magnesium may also be unsuitable in kidney failure.

For this reason, do not use a bowel cleansing medicine from the pharmacy, or one you have used before, on your own decision.

The day before the procedure, in kidney disease

Take the colonoscopy preparation medicine your doctor has chosen according to your kidney function, following the dose and timing plan you have been given.

The timing of the last dose should be set taking into account your kidney function, any fluid restriction, your dialysis programme and the time of your procedure.

At the end of the preparation, the fluid passed is expected to become pale yellow or clear and to contain no solid stool.

Fluid intake in kidney disease

Taking enough fluid during bowel cleansing is important. But in patients with kidney disease the approach of “the more fluid you drink the better” is not correct.

Patients with:

• Advanced kidney failure,
• Dialysis treatment,
• Heart failure,
• Marked swelling of the legs,

or whose daily fluid intake has been restricted by their doctor, should not increase the recommended amount of fluid on their own initiative.

In these patients the amount of fluid that may be taken should be set individually by the doctor.

Regular medicines in kidney disease

Patients with kidney disease are often taking blood pressure medicines, water tablets and other medicines.

Tell your doctor the list of all the medicines you take before the colonoscopy.

Mention it in particular if you are taking:

• Water tablets (diuretics),
• Blood pressure medicines of the ACE inhibitor or ARB group,
• Painkillers or anti-inflammatory medicines,
• Diabetes medicines,
• Blood-thinning medicines.

Do not stop any of these medicines or change the dose on your own decision. Which of them are to be taken before the procedure should be decided by your doctor and, where needed, the anaesthetic team.

Patients on dialysis

In patients on haemodialysis or peritoneal dialysis, colonoscopy preparation should be planned together with the nephrology and gastroenterology teams and, where needed, the anaesthetic team.

The timing of the bowel cleansing and of the dialysis is arranged individually, taking into account the patient’s fluid balance, electrolytes and the medicines they take.

Patients on dialysis should not follow the standard colonoscopy preparation without consulting their doctor.

The day of the procedure, in kidney disease

Follow the fasting, fluid and medicine instructions you have been given.

If your preparation programme includes a dose to be taken on the morning of the procedure, take it only at the time you have been told.

If you have been advised to take your blood pressure medicine on the morning of the procedure, take it with a very small amount of water.

Important warnings in kidney disease

If you have kidney failure, do not choose the colonoscopy preparation medicine yourself.

In patients with kidney disease the aim is not only that the bowel should be well cleansed, but that in doing so kidney function, fluid balance and the levels of minerals in the blood are protected.

The preparation programme should therefore be arranged individually by your doctor according to the degree of your kidney disease.

Colonoscopy preparation in patients with diabetes

Patients with diabetes need particular care when preparing for a colonoscopy.

Eating less during the bowel cleansing, going without food for a long period, and the fluid loss caused by the bowel cleansing medicines can make the blood sugar fall lower or rise higher than usual.

For this reason the colonoscopy preparation of patients with diabetes, and the medicines they take, should be arranged individually.

What to mention when making an appointment, in diabetes

If you have diabetes, tell your doctor when you make the colonoscopy appointment:

• Whether you have type 1 or type 2 diabetes,
• The names and doses of the insulins you use,
• The diabetes medicines you take,
• Whether you use a continuous glucose monitor or an insulin pump,
• Whether you have previously had a serious fall in blood sugar while fasting,
• Whether you have kidney or heart disease.

The day before the procedure, in diabetes

Because your normal eating pattern will change during the colonoscopy preparation, your blood sugar may also be affected.

Take the colonoscopy preparation medicine you have been given according to the written dose and timing plan.

If part of the preparation is planned to be taken on the day of the procedure, your diabetes medicines and the length of your fast should be arranged accordingly by your doctor.

You may need to check your blood sugar more often than usual during the preparation.

Do not change the dose of your diabetes medicine or your insulin other than on your doctor’s advice.

The day of the procedure, in diabetes

Follow the fasting, clear fluid and medicine instructions you have been given.

If your preparation programme includes a dose to be taken on the morning of the procedure, take it only at the time you have been told. Do not take food, milk or drinks that are not clear unless your programme allows it.

It will be useful to measure your blood sugar on the morning of the procedure.

Whether you are to take your insulin or diabetes medicine on the morning of the procedure should be decided beforehand by your doctor.

Patients using insulin

In patients using insulin, one of the most important problems during colonoscopy preparation is an excessive fall in blood sugar (hypoglycaemia).

The rapid-acting insulins taken with meals in particular should not be given at the same dose when the patient is not eating.

By contrast, basal insulin should not be stopped altogether, particularly in patients with type 1 diabetes. Stopping insulin completely can lead to a serious rise in blood sugar and to ketoacidosis.

For this reason:

Do not change or completely stop your insulin dose on your own decision.

Before the colonoscopy your doctor should tell you which insulin to use, at what dose and at what time.

The pump settings of patients using an insulin pump should also be planned with their doctor before the procedure.

Patients taking diabetes tablets

The medicines used in the treatment of diabetes are not all the same.

Some can lower the blood sugar too far during a fast, while others can cause different problems during fluid loss or a long fast.

Tell the doctor planning the colonoscopy the names of the diabetes medicines you take.

Because you will be fasting on the day of the procedure, the use of your diabetes medicines may be rearranged by your doctor.

Patients taking SGLT2 inhibitors

Be sure to tell your doctor if you are taking any of the following medicines:

• Empagliflozin
• Dapagliflozin
• Canagliflozin
• Ertugliflozin

Together with a long fast, bowel cleansing and fluid loss, medicines in this group can uncommonly lead to a serious condition called diabetic ketoacidosis.

Moreover, the blood sugar is not always very high when this happens.

For this reason medicines of the SGLT2 group may need to be stopped temporarily before procedures that require planned anaesthesia.

When the medicine is to be stopped should be decided by your doctor.

Be sure to tell your doctor and the anaesthetic team the name of the medicine you take before the procedure.

Patients taking medicines of the GLP-1 group

Be sure to tell your doctor if you are taking the following medicines or similar ones:

• Semaglutide
• Dulaglutide
• Liraglutide
• Tirzepatide

These medicines may be used for weight control as well as for the treatment of diabetes.

Medicines of the GLP-1 group can slow the emptying of the stomach in some people.

This matters in procedures carried out under anaesthesia, because food remaining in the stomach can increase the risk of vomiting and of stomach contents passing into the lungs (aspiration).

Be sure to tell your doctor and the anaesthetic team before the procedure, particularly if:

• You have recently started the medicine,
• Your dose has recently been increased,
• You have nausea,
• You are being sick,
• You have marked bloating or indigestion,
• Your stomach is known to empty late.

Do not stop your GLP-1 medicine on your own decision.

Whether the medicine is continued or stopped temporarily should be decided by your doctor and the anaesthetic team according to the medicine you take and your individual risks.

Monitoring the blood sugar

It can be useful to check the blood sugar more often than usual during colonoscopy preparation.

Patients using insulin in particular should keep their blood glucose meter with them.

If symptoms suggesting a low blood sugar appear — shaking, sweating, palpitations, extreme hunger, dizziness, feeling faint or confusion — contact your healthcare team rather than continuing with the preparation.

Important warnings in diabetes

Patients with diabetes may not prepare for a colonoscopy on their standard medicine regimens.

In particular:

patients taking insulin, an SGLT2 inhibitor or a medicine of the GLP-1 group must tell their doctor about the medicines they take before the colonoscopy.

The aim, alongside cleansing the bowel well, is that during the preparation and the anaesthesia the blood sugar is kept at a safe level, fluid loss is prevented and the risk of aspiration is reduced.

Do not stop your medicines or change their doses on your own decision.

Colonoscopy preparation in patients with heart disease and those taking blood-thinning medicines

If you have heart disease or a stent in your coronary arteries, or if you take a blood-thinning medicine, your medicines must be assessed by a doctor before the colonoscopy.

Stopping blood-thinning medicines unnecessarily can increase the risk of a clot forming, of a heart attack or of a stroke. On the other hand, continuing some medicines can increase the risk of bleeding, particularly where a polyp has to be removed during the colonoscopy.

For this reason you must on no account stop your blood-thinning medicines on your own decision.

What to mention when making an appointment, in heart disease

Tell the doctor planning the colonoscopy if any of the following applies:

• Coronary artery disease,
• A previous heart attack,
• A coronary stent,
• Heart failure,
• A disturbance of heart rhythm,
• Atrial fibrillation,
• Heart valve disease,
• An artificial heart valve,
• A pacemaker or ICD,
• A previous stroke,
• A previous clot in the veins of the leg or in the lungs,
• Taking blood-thinning medicines.

If possible, bring a current list of all the medicines you take with you.

The blood-thinning medicines in use

Be sure to tell your doctor if you are taking any of the following:

Antiplatelet medicines

• Aspirin
• Clopidogrel
• Prasugrel
• Ticagrelor

Anticoagulant medicines

• Warfarin
• Apixaban
• Rivaroxaban
• Dabigatran
• Edoxaban
• Heparin or low molecular weight heparins

If you do not know the name of your medicine, bring the box or your list of medicines with you.

Taking aspirin

In most patients taking low-dose aspirin, the aspirin can be continued without being stopped before a routine colonoscopy.

If you are taking aspirin for cardiovascular disease, a previous heart attack or a coronary stent in particular, do not stop the medicine on your own decision.

If the removal of a large polyp or advanced endoscopic treatment is planned, the use of aspirin is assessed separately by the doctor.

Taking clopidogrel, prasugrel or ticagrelor

Whether these medicines are to be stopped before a colonoscopy must be decided by a doctor.

The bleeding risks of a purely diagnostic colonoscopy and of an intervention such as the removal of a polyp are not the same.

In patients who have recently had a stent placed in a coronary artery in particular, stopping these medicines without supervision can lead to a clot forming inside the stent and to a heart attack.

So if you have a stent:

Be sure to say “I have a stent and I take a blood thinner” when you make your appointment.

Where necessary, the decision about your medicine is made jointly by your cardiologist and your gastroenterologist.

Taking two blood thinners together

If you take two antiplatelet medicines together — aspirin plus clopidogrel, for instance, or a similar combination — do not stop your medicines yourself.

In patients who have recently had a heart attack or a coronary stent in particular, stopping these medicines can pose a serious risk.

The timing of the colonoscopy and how the medicines are to be arranged are planned, where needed, together with your cardiologist.

Taking warfarin

In patients taking warfarin, different arrangements may be needed according to the type of colonoscopy to be done and the risk of a clot forming.

If your doctor thinks it necessary, they may ask for an INR test before the procedure.

In some patients warfarin can be continued, while if an intervention carrying a high risk of bleeding is planned it may need to be stopped temporarily.

In some patients at high risk of clotting, heparin treatment may be needed during the changeover period.

Do not stop warfarin on your own decision, and do not start another blood thinner in its place yourself.

Taking blood thinners of the DOAC group

The effects of these medicines differ from those of warfarin, and the arrangements made before a procedure differ too.

When the medicine is to be stopped is decided according to:

• The medicine being taken,
• Your kidney function,
• Why you are taking the medicine,
• Your risk of a clot forming,
• Whether a procedure such as the removal of a polyp is to be carried out during the colonoscopy.

For this reason, do not act on your own decision along the lines of “I will stop my blood thinner the day before”.

In patients taking dabigatran in particular, kidney function can considerably affect how long the medicine takes to leave the body.

If you have heart failure

In patients with heart failure, the fluid loss and the changes in fluid and electrolytes that occur during bowel cleansing are important.

If you have heart failure, be sure to say so when you make your colonoscopy appointment.

Speak to your doctor before following the standard bowel preparation, particularly if:

• Your breathlessness has increased,
• There is marked swelling of your legs,
• You have recently been admitted to hospital with heart failure,
• Your daily fluid intake has been restricted by a doctor.

If you are on a fluid restriction, do not drink excessive amounts of fluid on your own decision during the bowel cleansing.

The day before the procedure, in heart disease

Take the bowel preparation medicine you have been advised according to the written dose and timing plan.

In patients with heart failure or on a fluid restriction, the type of preparation, the amount of fluid to be taken and the timing of the last dose should be set individually.

The day of the procedure, in heart disease

Follow the fasting and medicine instructions you have been given.

If your preparation programme includes a dose to be taken on the morning of the procedure, take it only at the time you have been told.

If you have been advised to take your blood pressure medicine on the morning of the procedure, take it with a very small amount of water.

Take your blood-thinning medicine only according to the doctor’s instructions given to you beforehand.

When is the blood thinner restarted?

This decision can vary according to what was done during the colonoscopy.

Simply having looked at the bowel is not the same as having had a large polyp removed.

For this reason, when you are to restart your blood-thinning medicine should be told to you when you are discharged.

Do not restart your medicine early on your own decision, and do not leave it stopped for longer than necessary.

Important warnings in heart disease

If you have heart disease, a coronary stent, an artificial heart valve or a disturbance of rhythm, or if you take any blood-thinning medicine, be sure to say so before the colonoscopy.

Do not stop your blood-thinning medicines on your own decision.