1. 8623-Colonoscopy (EN)

A colonoscopy is an examination of the whole large bowel. This leaflet explains what this examination entails and how you should prepare for it.


A colonoscopy is an examination of the whole large bowel. This procedure is performed by a gastroenterologist, house officer or nurse endoscopist using an endoscope. An endoscope is a flexible tube of one centimetre in diameter with a small camera attached to its end. The camera’s images are displayed on a monitor.

Conditions including inflammation, ulcers, polyps, bleeds and growths can be identified during the examination. A colonoscopy is sometimes used as a (routine) screening test. Pieces of tissue from the intestinal mucosa may also be removed during the examination, or it could include treatments, such as the removal of polyps. Such procedures are not painful.

To be able to assess whether your mucosa is healthy or abnormal, there should be no food residue in the bowel. That is because food residue could obstruct the view. If, during the examination, it turns out that your bowel is not clean, the examination may be unsuccessful and have to be repeated.

Preparation at home


Drinking a laxative will clear your bowel. Your GP will decide which is most suitable laxative for you. This will depend on, among other things, your medical history. You can collect the laxative using the prescription from your own pharmacy or the pharmacy in Isala Zwolle’s central lobby. Take the laxative as directed. It is important that you follow the directions. The directions and prescription will be sent to your home address as soon as you have been scheduled for the examination. The laxative will cause watery stools so it is important that you remain in the vicinity of a WC. You may experience headaches when taking the laxatives. You should therefore drink an extra 1.5 to 2 litres during the day. If the headache symptoms are very bad, you may take some paracetamol.

Eating and drinking

If you drink other liquids in addition to your laxatives, it is important that they are clear liquids. You must not drink carbonated liquids, milk, red fruit juices or lemonade, cloudy fruit juices or alcohol. Stop eating food containing pips and seeds three days before the examination. This is because they could block the endoscope. Directions setting out in detail what you can and can’t eat will be sent to your home address as soon as you have been scheduled for the examination.


The doctor will have agreed with you whether the examination is to take place with or with mild sedation. More information about sedation is available at will find that information at the bottom of the web page, under the heading 'Related leaflets'. It is important that you read this information carefully.

Your use of medication

Before carrying out the examination, it is important that we know what medication you are taking and are familiar with your medical history. We would therefore ask you to complete this digital questionnaire in as much detail as possible. Please state the name and dosages of your medication in the digital questionnaire.

Please note: 
  • If you take iron tablets, iron supplements or iron drinks, stop taking them 7 days before the examination. You may start taking the tablets or supplements again after the examination.
  • If you have diabetes, the admitting nurse will contact you before the examination. She will discuss with you how to take your medication in preparation for this examination. Bring your diabetes medication and glucose-monitoring device with you on the day of the examination.
  • If you use blood thinners, you may continue to take them unless the thrombosis service or admitting nurse contacts you.
  • If you have sleep apnoea and use a medical aid such as a CPAP device or an MRA appliance, bring it with you to the examination.
  • If you have a stoma and would like to speak to the stoma consultant about spare stoma equipment, please indicate this in the digital questionnaire.
  • You may continue to use any other medication. The admitting nurse will contact you if there is any medication you will need to stop taking.
  • Do not take your medication at the same time as the laxative. It is better to allow a 30-minute interval. The laxative could interfere with the absorption and action of medicines.

Important information to know if you use blood thinners

Using coumarins

The use of Sintrom (Acenocoumarol) or Marcoumar (Phenprocoumon) usually has to be stopped temporarily. It may sometimes be necessary to inject Fradoxi (Heparin) temporarily on the days when coumarins are not used. The thrombosis service will contact you about further instructions.

Using carbasalate calcium (Ascal) and acetylsalicylic acid (aspirin)

If you are coming for a colonoscopy and you take Ascal (acetylsalicylic acid), you may continue to take that medication. It does not increase the risk of haemorrhage during a colonoscopy.

Using other blood thinners

If you take Clopidogrel, also known as Plavix and Grepid, you may continue to take it unless you use it combination with another blood thinner. In that case, the admitting nurse will contact you.
If you take Ticagrelor, also known as Briliquie, the admitting nurse will contact you.

If you take Persantin, also known as dipyridamole, or if you use Asasantin (dipyridamole/acetylsalicylic acid) the admitting nurse will contact you about this.
If you use a DOAC (dabigatran/Pradaxa, rivaroxaban/Xarelto, apixaban/Eliquis, edoxaban/Lixiana), you will need to stop taking them before the examination. The thrombosis service will contact you about further instructions and tell you when to stop. We will register you in advance with the thrombosis service.

The day of the examination

Course of the examination

During the examination, you will be lying on your left side with your knees drawn up in a bed or on an examination table. Your lower body will be covered with a towel. If you are given mild sedation, your blood pressure will be measured and a clip will be attached to your finger to monitor your heart rate and your blood oxygen level during the examination. Make sure there is no nail polish on your fingers as this will impede the measurement of your blood oxygen levels. You will be given a sedative and/or a painkiller through an IV needle, causing you to feel drowsy and relaxed during the examination. This is not an anaesthetic. The fast action of the drug means the examination can take place almost immediately. The endoscope is covered with a special lubricant.

Following an internal examination, the specialist will carefully slide the tube in through the anus. Every now and then, some air (CO2) will be introduced into the large bowel. This causes the large bowel to distend and allows the doctor to have a good look at it. You may experience painful intestinal cramps owing to the introduction of air and the turns made with the endoscope. This will probably cause you to break wind during, and also often after, the examination. This is perfectly normal.
If necessary, the specialist may remove some pieces of mucosa for further analysis. He may also remove polyps or perform another treatment. The procedure will last around half an hour.

If one or more (large) polyps are found during the colonoscopy, the specialist may decide not to remove all of them in a single session. You will then be scheduled for a follow-up colonoscopy. This is for quality- and safety-related reasons.

After the examination

If you have been sedated and/or given a painkiller, you will usually spend another hour in the Day Care ward, until you are properly awake and are not experiencing any symptoms. You will be given a light snack in the ward. Your contact person will then be telephoned to come and collect you. You won't be allowed to go home on your own if you have been sedated. You will be under the influence of the sedative for the first 24 hours after the examination and you are not allowed to drive. You may use a taxi or public transport only if someone is accompanying you!
If you have not been sedated or given a painkiller, you may - provided you are not experiencing any symptoms - go home under your own steam fairly soon after the examination.

You may still experience some watery stools, abdominal pain and flatulence after the examination. We recommend that you bring some spare underclothes and clothing with you. You can start eating and drinking again as normal after the examination.


The doctor who carried out the examination will give you a verbal and written account of the provisional results. The final results will be sent to the GP who requested the examination. If a medical specialist requested the examination, it will usually be followed by an outpatient’s appointment or a telephone appointment.
You will be given details of follow-up appointments when you go home.

Possible complications

A colonoscopy is a relative safe procedure. On average, a serious complication occurs twice in every thousand procedures. For instance, a tear may occur in the intestinal wall during the examination. This is more likely if the large bowel is severely inflamed, or if there is a large number of protuberances.
A tear may also occur after the removal of a polyp. The main symptoms to occur are abdominal pain and fever. The removal of a polyp may also result in a haemorrhage. This can happen during the examination, but also up to fourteen days afterwards. In the event of heavy blood loss or other symptoms after the examination, you may contact the endoscopy department or the gastroenterologist on duty through reception. You will be given these instructions after the examination.

Information video

The Colonoscopy information video shows you how the examination is carried out. Make sure you watch the video before your examination.

Voorlichtingsfilm Colonoscopie


If you have any questions, please telephone the Endoscopy Department of the Gastroenterology Outpatients’ Clinic.


+31 (0) 88 624 33 20 (available from Monday to Friday from 8:30 to 10:30)

Deze brochure is ook beschikbaar in Nederlands: folder Dikke darmonderzoek (Colonoscopie)

Laatst gewijzigd 11 juli 2023 / 8623