The Different Types Of Colonoscopies

  • Stephanie Jolliffe BSc (Hons), The University of Manchester, United Kingdom
  • Ellen Rogers MSc in Advanced Biological Sciences, University of Exeter


Endoscopies are medical procedures that allow medical professionals to examine your body’s internal organs.1 They involve medical professionals passing a very small camera, attached to a tube, through your body. There are several different types of endoscopies, each of which are used to examine a different internal organ. 

A colonoscopy is a type of endoscopy used to examine your colon and rectum, which together form your large intestine. There are several different types of colonoscopies that can be carried out for diagnostic, therapeutic, or screening purposes.2 However, the type of colonoscopy you may require depends on the purpose of the colonoscopy and other factors, such as your medical status and medical history. 

Types of colonoscopies

Screening colonoscopy

A screening colonoscopy is used to check for cancer in your colon or rectum when you do not have cancer symptoms. Colorectal cancer is the third most common type of cancer, and anyone can get it - although some people are more at risk of developing it.3 Therefore, a screening colonoscopy can be really important in checking for any suspicious tissue in your colon and rectum. When treating cancer, it is vital to catch it in its earlier stages to have a better chance of being able to treat it. 

Usually, you will start being invited for regular screening colonoscopies when you reach 45 years of age.4 However, if you are someone who has an increased risk of developing colorectal cancer, these visits may start earlier. Known risk criteria for colorectal cancer include:

If when the medical professional carrying out your colonoscopy finds any polyps or suspicious tissues, they may remove them in the same session. The removed tissue will be sent for testing to see if it is cancerous or not. 

Screening is also carried out on individuals who have been treated for colorectal cancer before. This is so that doctors can monitor how you have been getting on since treatment and keep an eye on things in case of remission.5  

Preparing for a screening colonoscopy 

Every type of colonoscopy requires an empty colon so that there are no obstructions present that hide polyps or leave images unclear. An empty colon also makes the process of having a colonoscopy run more smoothly as it will take less time, reducing the risk of complications.6

Your doctor will provide you with instructions on how to prepare for your colonoscopy. Make sure that you read these instructions carefully and ask your doctor to clarify anything that you do not understand. Whilst these instructions may vary between doctors and patients, the general preparation instructions are as follows:

A few days before:

  • Eat a low-fibre diet 

The day before:

  • Go on a clear liquid diet (coffee or tea with no milk, water, or clear soup). 
  • Take the laxatives that your doctor prescribes the evening before your colonoscopy. This will trigger diarrhoea, emptying your bowels

The day of the colonoscopy:

  • Maintain a clear liquid diet
  • Do not consume anything (food or liquid) two hours before your colonoscopy5

Possible risks and complications of screening colonoscopies include:

  • Tears in the colon wall
  • Infection
  • Unusual reactions to anaesthetic
  • Bleeding2

Diagnostic colonoscopy

A colonoscopy that is done to try to find the cause of the symptoms you may be experiencing is known as a diagnostic colonoscopy. From the images taken, doctors may be able to diagnose the cause of your symptoms and provide you with the appropriate treatment and management options going forward. 

Symptoms that may lead your medical professional to request that you get a diagnostic colonoscopy include:

  • Persistent diarrhoea or constipation
  • Bleeding from your rectum
  • Blood in your stools
  • Sudden, inexplicable weight loss
  • Unexplained fatigue
  • Abdominal pain that does not go away.7

Medical professionals can diagnose the cause of your symptoms and treat it in the same colonoscopy session. For example, if they find that polyps in your colon are the root of your problem, they may remove those polyps then and there. As such, doctors have several instruments that they may use during a colonoscopy to remove tumours and polyps, among other things. However, for more advanced cancers or tumours that have spread to other organs, doctors may insert a stent into your colon to help keep it open.

The preparation for a diagnostic colonoscopy is generally the same as that for a screening colonoscopy.


A sigmoidoscopy is used to examine your rectum and the lower part of your colon and can be used for both screening and diagnostic purposes. It screens for colorectal cancer and can be used to diagnose conditions that may be affecting your bowel. The main difference between a sigmoidoscopy and a colonoscopy is that a sigmoidoscopy only examines your rectum and the lower part of your colon rather than your whole colon. Therefore, a sigmoidoscopy is less invasive than a conventional colonoscopy.8

Symptoms that may lead your medical professional to request that you get a diagnostic colonoscopy include:

  • Diarrhoea
  • Stomach pain
  • Constipation
  • Bleeding from your rectum

Preparing for a sigmoidoscopy

Like with the screening and diagnostic colonoscopies, your healthcare professionals should give you a detailed sheet of instructions describing how you should prepare for your sigmoidoscopy. Make sure you ask about any instructions that you need clarification on.

Generally, you will be required to take a laxative to help empty your bowel. However, you may also be told to refrain from eating certain foods a few days before your test.

Day of sigmoidoscopy:

  • You will be given a hospital gown to change into
  • The examiner will ask you to lie on your side on the exam table
  • Anaesthesia is usually not given for sigmoidoscopies; however, you may be given medication that may make you drowsy and get your muscles to relax during the procedure
  • The doctor will put a thin tube up through your rectum
  • The tube will be used to inflate your colon slightly so that images come out clearer
  • The doctor will then push the tube further up into your lower colon
  • Any polyps that are found will be removed and sent for testing

Virtual colonoscopy

A virtual colonoscopy involves obtaining pictures of your colon and rectum using X-rays. As the pictures are taken from outside your body, this procedure is non-invasive.10 Like the other types, virtual colonoscopies are used to check for polyps and abnormalities in your rectum and colon. Virtual colonoscopies may be preferred over conventional colonoscopies for people on blood thinning medication or with medical conditions that make conventional colonoscopies unsuitable for them. 

Preparing for a virtual colonoscopy

It is best to speak to your doctor for specific instructions. Be sure to let your doctor know about any medications that you are taking and any personal medical devices you may have. It is also very important to let your doctor know if you are (or might be) pregnant.

Before the virtual colonoscopy:

  • Adjust your diet - you may be required to go on a clear liquid diet (fat-free broths, black tea and coffee, water).
  • You may be required to take a laxative to empty out your bowels. 
  • Drink a contrast medium that will allow your rectum and colon to be visible under the X-ray.

After a virtual colonoscopy:

  • You may feel bloated for a few hours
  • You may resume regular activities straight away
  • You may go back to your regular diet

Key differences between types of colonoscopies

Scope of examinationLength of procedurePreparationPrivate cost (estimated)
ColonoscopyRectum and entire colon20-60 minutes12,13Full bowel preparation
Clear liquid diet for a few days pre-procedure
Sedation and anaesthetic
£1,807- 2,418 
SigmoidoscoyRectum and lower colon only15-20 minutes8Bowel preparation (not as extensive as a colonoscopy)
Clear liquid diet for a few days pre-procedure 
Virtual colonoscopyRectum and entire colon10-15 minutes14Laxative and contrast medium to be taken the night before£840+


Various types of colonoscopies exist, including screening colonoscopies, diagnostic colonoscopies, sigmoidoscopies and virtual colonoscopies. Despite their differences, they are all used to screen for colorectal cancer and to also diagnose the cause of certain symptoms you may be experiencing. These symptoms include bleeding from the rectum, stomach pain, persistent diarrhoea, and constipation. The type of colonoscopy that you will receive depends on several factors, including your medical status as well as which area of your colon medical professionals are interested in examining. If you have any further questions about colonoscopies or colorectal cancer, you should speak to your doctor.


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  2. Cleveland Clinic. Colonoscopy | Cleveland Clinic [Internet]. Cleveland Clinic. 2019. [Cited 2023 Apr 14]. Available at:
  3. Recio-Boiles A, Waheed A, Cagir B. Colon cancer [Internet]. StatPearls Publishing; 2019. Available at:
  4. Centers for Disease Control and Prevention. What Should I Know About Screening for Colorectal Cancer? [Internet]. 2019. [Cited 2023 Apr 14]. Available at:
  5. Cancer Research UK. Colonoscopy | Bowel cancer | Cancer Research UK [Internet]. [Cited 2023 Apr 14]. Available at:
  6. Harvard Health Publishing. Preparing for a colonoscopy - Harvard Health [Internet]. 2018. [Cited 2023 Apr 14]. Available at:
  7. NHS. Colonoscopy - Why it’s done [Internet]. 2019. [Cited 2023 Apr 14]. Available at:
  8. Cancer Net. Sigmoidoscopy [Internet]. 2013. [Cited 2023 Apr 14]. Available at:
  9. Johns Hopkins Medicine. Sigmoidoscopy [Internet]. 2019. [Cited 2023 Apr 14]. Available at:
  10. National Institute of Diabetes nd Digestive and Kidney Diseases. Virtual Colonoscopy [Internet]. [Cited 2023 Apr 14]. Available at:
  11. Mayo Clinic. Flexible Sigmoidoscopy [Internet]. 2018. Available at:
  12. UCLA Health. What to Expect on the Day of Your Colonoscopy - Colorectal Cancer Screening [Internet]. 2023. [Cited 2023 Apr 14]. Available at:
  13. Colorectal Cancer Alliance. How long does a colonoscopy take? [Internet]. [Cited 2023 Apr 14]. Available at:
  14. Johns Hopkins Medicine. Virtual Colonoscopy [Internet]. [Cited 2023 Apr 14]. Available at:
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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