Virtual colonoscopy

Your health expert: Dr Ian McCafferty, Consultant Radiologist
Content editor review by Pippa Coulter, October 2022
Next review due October 2025

A virtual colonoscopy is a procedure that uses CT scans to look inside your large bowel. It’s also known as CT colonography or CT colonoscopy. It’s used to check your large bowel for growths or signs of cancer, and to investigate bowel symptoms.

About virtual colonoscopy

A virtual colonoscopy is an alternative procedure to a traditional colonoscopy – the usual test for examining your large bowel. A traditional colonoscopy uses a camera inserted into your back passage to look at your large bowel. Virtual colonoscopy is as good at picking up bowel cancer as traditional colonoscopy. But it’s less invasive and tends to be more comfortable.

Reasons for having a bowel procedure

Reasons for needing to look inside your large bowel include the following.

As part of the national bowel cancer screening programme in England, if initial tests have found blood in your poo.
Investigating symptoms that suggest bowel cancer. These might include bleeding from your bottom or a change in bowel habit, like needing to poo more often, diarrhoea or constipation.
You have a strong family history of bowel cancer. This could be if two or more first-degree relatives have had bowel cancer or one relative under the age of 45 has had it.

Who can have a virtual colonoscopy?

There are various reasons why you might be offered a virtual colonoscopy instead of a traditional colonoscopy. These include if you have health issues or mobility needs that might make a traditional colonoscopy difficult or unsafe. You may also be offered a virtual colonoscopy if you previously had a colonoscopy, but it failed to see all of the large bowel. You may also have virtual colonoscopy as part of a private bowel cancer screening test.

Who can’t have a virtual colonoscopy?

Not everyone can have a virtual colonoscopy. Your doctor won’t usually recommend it if you:

have an active flare-up of inflammatory bowel disease such as Crohn’s disease or ulcerative colitis
have diverticulitis and diverticulosis
have recently had abdominal surgery
are a child or young adult

Having a virtual colonoscopy depends on the procedure being available at your hospital.

Your doctor will be able to tell you why they recommend a virtual colonoscopy. They’ll explain exactly what to expect when you have the procedure and may give you some information to take away. Be sure to ask your doctor any questions you have. It's important that you feel fully informed because you’ll need to give your consent to go ahead with the procedure.

Preparation for virtual colonoscopy

You’ll have a virtual colonoscopy in the CT scanning department at a hospital as an outpatient. This means you have the test and go home the same day. A radiographer (a health professional trained in CT scans) or a doctor called a radiologist may carry out your procedure.

Your hospital will give you detailed information about how to prepare for your test. This may include the following.

Clearing your bowel

Your bowel usually needs to be empty for a virtual colonoscopy. This is so the pictures produced are as clear as possible. The hospital may ask you to take one of the following to help clear your bowel.

A strong medicine called a laxative that you’ll usually need to take the day or evening before your virtual colonoscopy.
A special liquid dye that you’ll need to drink over the day or two before your test. This mixes with your poo but also acts as a laxative. It helps to show up any abnormalities in your large bowel.

Laxatives clear your bowel by making you need to poo. They can quickly give you diarrhoea, so make sure you stay close to a toilet after you take them.

What to eat and drink

Your hospital may also give you some instructions about what you can eat or drink before the procedure. This might include only eating low-fibre foods for a day or two beforehand, and sticking to clear fluids like water, squash or black tea or coffee.

Medications to stop

You may need to stop certain medicines before having a virtual colonoscopy. These may include iron supplements and other medicines that can cause constipation. Let your doctor know if you’re taking anything like this before your virtual colonoscopy. They can advise if you need to stop taking them, and for how long.

Virtual colonoscopy procedure

A virtual colonoscopy may take up to 30 minutes, but you’ll be in the department for longer – usually an hour or so. When you’re ready, you’ll be given a hospital gown to change into. You’ll meet with the doctor or radiographer performing the procedure. They’ll check that you’re happy to give your consent to go ahead.

You won’t need an anaesthetic or sedative for a virtual colonoscopy. Your radiographer will ask you to lie on your side on the scanning table. They’ll place a fine tube (a cannula) into a vein in the back of your hand. Your doctor will give you a medicine to relax your bowel. Sometimes, you may also have an injection of dye (contrast) to show up your bowel and surrounding structures. This might make you feel hot for a few minutes and give you a strange, metallic taste in your mouth. But it should pass quickly.

Your radiographer will gently pass a small tube into your back passage. They’ll use this to pump gas into your bowel to inflate it so it can be seen more clearly on the scan. You may feel some slight discomfort when this happens, but it isn’t usually painful.

Your radiographer will then move the scanning table into the tunnel of the CT scanner. They’ll take scans while you’re lying on your back and then ask you to lie on your front or side and take some more. They might also ask you to hold your breath for a few seconds at certain points during the scan. It’s important to try to lie very still during the scan.

Worried about your colon health?

Get a picture of your current health and potential future health risks with one of our health assessments.

To book or to make an enquiry, call us on 0345 600 3458^∧

Find out more about colon health assessments

Aftercare for virtual colonoscopy

You may need to wait in the CT scanning department for a short period of time (15 to 30 minutes) after your scan. This is normally if you’ve had an injection of dye or medicine to relax your bowel. Otherwise, you’ll be able to change and go home as soon as you feel ready. Sometimes, the medicine used to relax your bowel can cause blurry vision. If this happens, you’ll need to wait until your vision has returned to normal – normally an hour or so – before you can drive.

After your virtual colonoscopy, you should be able to eat and drink normally, and return to your usual activities straight away. You might feel a bit bloated and have pain in your tummy for a short time after the test. This is due to the air that was pumped into your bowel during the procedure. It doesn’t usually last long, but you can take over-the-counter painkillers if you need to. The hospital staff will tell you about any other side-effects to look out for and how to manage them.

Getting your results

Your scans will be analysed by a specialist doctor called a radiologist. They’ll send the results to whoever referred you for the virtual colonoscopy. This can take up to a week or two. There are several possibilities of what your virtual colonoscopy may show.

Polyps. These are growths that can develop in the lining of your bowel. There’s a small chance that, over time, they may grow into a cancer. Your doctor may recommend a standard colonoscopy to take a closer look and remove them.
Signs of bowel cancer. If this happens, you’re likely to need further tests to confirm a diagnosis. Sometimes, you may be offered further scans on the same day as your virtual colonoscopy.
Diverticulosis. These are small pouches in the lining of your bowel that can become inflamed and infected.
The test may not find a cause for your symptoms. Your doctor may sometimes recommend further tests, such as a traditional colonoscopy, to have a closer look at your bowel.

Complications of virtual colonoscopy

Complications are when problems occur during or after the procedure. Complications from virtual colonoscopy are uncommon but may include the following.

Feeling faint. The medicine used to relax your bowel can sometimes cause low blood pressure and a slow heart rate. This can make you feel faint.
Allergic reaction to the contrast medium. This is very rare. But if you feel unwell or find it difficult to breathe during the test, tell the radiographer or doctor doing your test straight away.
Damage to your bowel. There’s a very small risk of your bowel being damaged or torn during the procedure. It’s been estimated that this happens in around 1 in3,000 people who have a virtual colonoscopy. If it did happen, you may need an operation to repair the tear.

CT scanners use X-rays to produce images, so you’ll be exposed to a small amount of radiation. If you’re pregnant or think you could be, let your doctor know because they may recommend an alternative test. Your doctor may recommend avoiding a CT scan if you’re pregnant because your baby is sensitive to the potential effects of radiation. They may suggest a traditional colonoscopy instead.

Alternatives to virtual colonoscopy

If you’re unable to have a virtual colonoscopy, your doctor may recommend having a CT scan of your abdomen and pelvis. This is done with a dye to show up parts of your bowel.

At some hospitals, you may be offered a newer kind of test, called a capsule endoscopy if you have symptoms of bowel cancer. This involves swallowing a capsule that contains a small disposable camera. The camera takes pictures as it travels along the length of your bowel. These are transmitted wirelessly to a data recorder, which your doctor will then review. You’ll need to take laxatives and restrict what you eat and drink the day before taking the capsule. If the test identifies any problems, you may still need to have a colonoscopy.

Capsule endoscopy isn’t available in all hospitals. Which test you are offered will depend on your circumstances, and what’s available at your local hospital. Your doctor will talk to you about the options available and which is best for you.

You don’t need an anaesthetic or a sedative for a virtual colonoscopy. This means you’ll be awake during the procedure. It can be a bit uncomfortable, but isn’t usually painful. Find out more in our section on the procedure.

You may have a bit of discomfort when the radiographer pumps gas into your bowel but this isn’t usually painful. Your tummy might feel a bit painful and bloated afterwards but this wears off quickly. You can read more in our sections on the procedure and aftercare.

The benefits of each type of colonoscopy depend on your personal circumstances. The two tests are equally good at picking up bowel cancer. A virtual colonoscopy is less invasive and you don’t need sedation. This means it can be a better option for elderly or frail people. But you can only have a biopsy (sample of tissue) or polyps removed with a standard colonoscopy. See our About section for more information on reasons for having one test or the other.

Studies have shown that virtual colonoscopy can pick up bowel cancer in more than 9 in 10 people who have large polyps (over 10 mm). This is as good as standard colonoscopy. But virtual colonoscopy is not as good as traditional colonoscopy at detecting smaller or flat polyps.

More on tis topic

Did our Virtual colonoscopy information help you?

We’d love to hear what you think.^∧ Our short survey takes just a few minutes to complete and helps us to keep improving our health information.

^∧The health information on this page is intended for informational purposes only. We do not endorse any commercial products, or include Bupa's fees for treatments and/or services. For more information about prices visit: www.bupa.co.uk/health/payg

Complete 2 mins survey

This information was published by Bupa's Health Content Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals and deemed accurate on the date of review. Photos are only for illustrative purposes and do not reflect every presentation of a condition.

Any information about a treatment or procedure is generic, and does not necessarily describe that treatment or procedure as delivered by Bupa or its associated providers.

The information contained on this page and in any third party websites referred to on this page is not intended nor implied to be a substitute for professional medical advice nor is it intended to be for medical diagnosis or treatment. Third party websites are not owned or controlled by Bupa and any individual may be able to access and post messages on them. Bupa is not responsible for the content or availability of these third party websites. We do not accept advertising on this page.

CT colonography. Cancer Research UK. www.cancerresearchuk.org, last reviewed 5 March 2019
Bowel cancer screening: guidelines for CTC imaging. Public Health England. www.gov.uk, updated 12 March 2021
Standards of practice for computed tomography colonography (CTC). Joint guidance from the British Society of Gastrointestinal and Abdominal Radiology and The Royal College of Radiologists, www.rcr.ac.uk, published January 2021
Colorectal assessment. Colorectal Surgery. Oxford Academic. academic.oup.com, published online August 2021
Spada C, Hassan C, Bellini D, et al. Imaging alternatives to colonoscopy: CT colonography and colon capsule. European Society of Gastrointestinal Endoscopy (ESGE) and European Society of Gastrointestinal and Abdominal Radiology (ESGAR) Guideline – Update 2020. Eur Radiol 2021; 31(5):2967–82. doi: 10.1007/s00330-020-07413-4
Bowel cancer screening: having a colonoscopy. Public Health England. www.gov.uk, updated 31 October 2021
Colorectal cancer. BMJ Best Practice. bestpractice.bmj.com, last reviewed 18 April 2022
Gastrointestinal tract (lower) cancers – recognition and referral. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised February 2021
Symptoms of bowel cancer. Bowel Cancer UK. www.bowelcanceruk.org.uk, reviewed June 2019
Gastrointestinal medicine. Oxford Handbook of General Practice. Oxford Academic. academic.oup.com, published June 2020
Colorectal surgery. Oxford Handbook of Clinical Surgery. Oxford Academic. academic.oup.com, published online November 2021
Diverticular disease. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised December 2021
Oakland K, Chadwick G, East JE, et al. Diagnosis and management of acute lower gastrointestinal bleeding: guidelines from the British Society of Gastroenterology. Gut 2019; 68:776–89
Colon capsule endoscopy. Cancer Research UK. www.cancerresearchuk.org, last reviewed 6 December 2021

Our information has been awarded the PIF tick for trustworthy health information.