Colonoscopy
A test where a thin, flexible camera is passed into the back passage to look at the lining of the whole large bowel, find the cause of symptoms, take samples and remove polyps.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- A colonoscopy lets the bowel lining be examined directly, with samples taken and polyps removed in the same test.
- It is thorough but not perfect — a clean bowel matters, some polyps can be missed, and a normal test does not guarantee nothing will ever develop.
- It is usually a day case; camera findings are often explained on the day, but biopsy results take about 1–2 weeks.
- The main practical points are the bowel preparation (a strong laxative) beforehand and, if you choose sedation, arranging someone to take you home and not driving for 24 hours.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Looks directly at the whole large bowel lining, which is one of the most thorough ways to examine it
People who are too unwell or unstable to undergo the test safely, until their condition is optimised.
You rest in a recovery area while any sedation wears off and the trapped air passes. Passing wind is normal and helps the bloating settle.
Clear written instructions and a named contact or unit number for problems at home.
You rest in a recovery area while any sedation wears off and the trapped air passes. Passing wind is normal and...
You can usually eat and drink normally. If you had sedation, go home with a responsible adult, rest, and do not...
Most people return to normal activities and work. Mild bloating or a little spotting of blood from the back...
Results from any biopsies or removed polyps are usually ready and explained by your team, along with any plan for...
What is a colonoscopy?
A colonoscopy is a test that lets a doctor or specialist nurse (the endoscopist) look directly at the lining of your large bowel (colon and rectum). A long, thin, flexible tube with a tiny camera and light is gently passed in through the back passage and guided around the bowel, with the pictures shown on a screen.
It is used to find the cause of symptoms such as bleeding from the bottom, a change in bowel habit, tummy pain, or unexplained weight loss or tiredness; as part of bowel cancer screening; and to keep an eye on conditions such as inflammatory bowel disease. During the test the endoscopist can take small tissue samples (biopsies) and remove growths called polyps, which can sometimes turn into cancer over time.
A colonoscopy is one of the most thorough ways to examine the bowel, but it is not perfect: the view depends on how clean the bowel is, some polyps can be missed, and occasionally the camera cannot reach all the way around. Good bowel preparation and an experienced endoscopist matter a great deal.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Colonoscopy compared with CT colonography
| Colonoscopy | CT colonography | |
|---|---|---|
| What it is | Camera inside the bowel | CT scan of the bowel |
| Take samples / remove polyps | Yes, in the same test | No — a colonoscopy is still needed if found |
| Radiation | None | Yes (X-rays) |
| Bowel prep | Yes | Yes (plus gas to inflate) |
| Sedation | Often offered | Not usually needed |
CT colonography may be used when colonoscopy is incomplete or unsuitable. If it finds a polyp, a colonoscopy is usually still needed to remove it. Your team will advise which suits you.
Preparing for your procedure
- Follow the bowel preparation instructions carefully — you take a strong laxative beforehand so the bowel is empty; poor preparation can mean polyps or cancers are missed or the test must be repeated.
- Follow the diet advice in the days before (often low-fibre, then clear fluids) and stay well hydrated as directed.
- Tell the unit about all your medicines, especially blood thinners, diabetes medicines and iron tablets, as some need stopping or adjusting before the test.
- Mention heart, lung or kidney conditions, diabetes, or any reaction to sedation, as these affect your sedation choice and monitoring.
- Decide in advance whether you want sedation, gas and air, or no sedation, and discuss the pros and cons with the team.
- If you choose sedation, arrange for a responsible adult to take you home and stay with you, and do not plan to drive, work or sign anything important for 24 hours.
- Allow several hours for the appointment, including preparation and recovery time, and wear comfortable clothing.
What happens
After checking your details and consent, you change into a gown and lie on your left side on a trolley with your knees bent. A clip on your finger monitors your pulse and oxygen, and if you have chosen sedation it is given through a small cannula in your arm.
The endoscopist gently passes the flexible camera in through the back passage and guides it around the bowel, using a little air or carbon dioxide to open up the view. You may feel bloating, cramping or an urge to pass wind — this is normal. If polyps are found they can usually be removed there and then, and small samples may be taken; these are usually not painful.
The test itself usually takes about 30–60 minutes. Afterwards you rest in a recovery area until any sedation wears off and the trapped air settles. The endoscopist can often tell you what they saw on the day, while results from any biopsies or removed polyps follow later.
Is this procedure right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- People who are too unwell or unstable to undergo the test safely, until their condition is optimised.
- Suspected bowel perforation or severe active colitis, where colonoscopy can be dangerous and other management is needed first.
- When a less invasive test (such as a FIT stool test, CT colonography or flexible sigmoidoscopy) would answer the question for that person.
- People who cannot complete the bowel preparation safely, where an alternative may be more appropriate.
Delay or rearrange if…
- You have an active gut infection, severe flare of colitis, or significant uncontrolled illness.
- Your blood thinners or diabetes medicines have not been properly planned around the test.
- Pregnancy, unless the test is genuinely needed and the timing has been discussed.
- You cannot arrange a responsible adult to take you home if you have chosen sedation.
- The bowel preparation has been inadequate, as the test would likely be incomplete or unreliable.
Alternatives to discuss
- No test, or watchful waiting, if symptoms are mild and the result would not change management.
- FIT stool test as a first-line check for many people with lower-risk symptoms or for screening.
- CT colonography for those in whom colonoscopy is unsuitable or incomplete.
- Flexible sigmoidoscopy when only the lower bowel needs examining.
- Going through an NHS pathway rather than self-funding, where time allows.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Comfort, sedation or contrast choices
If local anaesthetic, sedation, contrast or pain relief is used, ask what is planned, why, and what it means afterwards.
Benefits
- Looks directly at the whole large bowel lining, which is one of the most thorough ways to examine it
- Can find the cause of bleeding, changed bowel habit, pain, anaemia or weight loss
- Can take samples and remove polyps in the same test, which can prevent some bowel cancers
- Can detect bowel cancer early, when treatment is more likely to succeed
- A clear, complete and well-prepared test can be reassuring and reduce the need for other investigations
Risks & complications
- Bloating, wind and cramping for a few hours after the test
- Feeling tired or groggy for the rest of the day if you have sedation
- A small amount of bleeding from the back passage, especially if a polyp was removed or a biopsy taken
- Discomfort or unpleasantness from the bowel preparation beforehand
- An incomplete test if the bowel is not clean enough or the camera cannot reach all the way around, sometimes needing a repeat or a different test
- A polyp or early cancer being missed, as no test sees everything
- More noticeable bleeding after polyp removal, which usually settles on its own
- Breathing, heart-rate or blood-pressure effects from sedation that need monitoring
- A tear (perforation) in the bowel wall, which can need treatment or an operation
- Heavy bleeding that needs admission to hospital, a transfusion or further treatment
- A serious reaction to the sedation
- Dehydration or salt imbalance from the bowel preparation, more likely in frail or older people
Colonoscopy is generally low-risk, but the serious risks — a tear in the bowel and significant bleeding — are real and slightly higher when polyps are removed. Sedation adds small risks of its own. The other key limitation is a missed polyp or an incomplete test, which is why bowel preparation and an experienced endoscopist matter. Ask about the unit's completion and detection rates and how complications would be handled.
Published figures to discuss
Serious complications are uncommon, but they increase when polyps are removed (therapeutic colonoscopy) compared with a purely diagnostic test, and depend on the patient's health, the bowel preparation, and the endoscopist's experience. 'Miss rates' for polyps reflect the test's limits rather than negligence and vary with preparation quality, withdrawal time and lesion size. Figures below are cautious ranges drawn from UK and international data.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Perforation (tear in the bowel wall) | Roughly 1 in 1,000 overall (UK audits report about 0.1%); higher when polyps are removed | Rare but serious; may need treatment or an operation. Risk rises with larger or more complex polyp removal. | NHS — Colonoscopynhs.ukPublished figure |
| Significant bleeding | Uncommon after a diagnostic test; reported around 1 in 50 after polyp removal in some sources | Usually settles on its own; occasionally needs admission, a transfusion or further treatment, and can occur up to about two weeks later. | NHS — Colonoscopynhs.ukPublished figure |
| Sedation-related breathing or heart effects | Around 1 in 200 procedures, usually not serious | Monitored throughout; risk is higher with deeper sedation and in people with heart or lung conditions. | NHS — Colonoscopynhs.ukPublished figure |
| Missed polyps / adenomas | Reported miss rates of roughly 1 in 8 to 1 in 4 for adenomas, higher for small or flat lesions | Reflects the test's limits; good preparation, adequate withdrawal time and an experienced endoscopist reduce it. | NHS — Colonoscopynhs.ukPublished figure |
| Incomplete examination (camera not reaching the caecum) | UK quality standards target completion in at least 90% of cases | An incomplete test may need a repeat or a CT colonography to see the rest of the bowel. | NHS — Colonoscopynhs.ukPublished figure |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
Most people feel back to normal within a day. There is no wound to heal, but you may have bloating and tiredness, and if you had sedation you will need to take it easy and not drive for 24 hours. The main thing you may be waiting for is the biopsy result.
- Bloating, wind and mild cramping that eases as trapped air passes
- Feeling tired or 'not quite yourself' for the rest of the day after sedation
- A small amount of blood from the back passage, especially after a polyp removal or biopsy
- Looser bowel motions for a short time after the bowel preparation
Aftercare
- Rest for the remainder of the day and drink plenty of fluids to rehydrate after the preparation.
- Eat light, normal meals when you feel ready unless told otherwise.
- If you had sedation, have a responsible adult with you and do not drive, operate machinery, drink alcohol or make important decisions for 24 hours.
- Avoid heavy lifting or strenuous exercise for a day or two if a polyp was removed, as advised.
- Expect a little wind and bloating, and mild spotting of blood if you had a polyp removed or a biopsy.
- Make a note of what the endoscopist told you and when and how you will get any biopsy results.
- Keep the unit's contact number to hand and use it if you have any warning signs.
- Bowel preparation collected and instructions understood
- Blood thinners and diabetes medicines discussed and adjusted if needed
- Sedation choice decided, with someone to take you home if you choose it
- A responsible adult to stay with you for 24 hours after sedation
- Time off arranged for the day of the test
- The unit's contact number saved for after the test
- Clear plan for how you will get your biopsy results
⚠ Get urgent help if…
- Severe or worsening tummy pain, or a hard, swollen, tender tummy
- Heavy or continuing bleeding from the back passage, or passing large clots
- A high temperature, chills or feeling very unwell
- Being unable to pass wind together with significant pain and swelling
- Feeling faint, breathless or having chest pain
- Persistent vomiting
- Any symptom your unit specifically warned you to report — contact them or seek urgent care
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
Often the endoscopist can tell you what they saw on the day — for example whether the bowel looked normal, whether polyps were found and removed, or whether there are signs of inflammation. Results from biopsies or removed polyps are examined under a microscope and usually take about 1–2 weeks.
A normal, complete colonoscopy is reassuring and makes serious bowel disease much less likely, but it does not guarantee nothing will ever develop, and no test finds every polyp. If your symptoms continue despite a normal result, go back to your doctor. Your team should explain what the findings mean for you, including any treatment, repeat test, or interval for future surveillance.
A colonoscopy reflects the state of your bowel on the day. How long the reassurance lasts depends on your risk: people at average risk with a normal screening test are usually rechecked after several years, while those with polyps, inflammatory bowel disease or a family history may need closer surveillance. Your team will advise the right interval; new or changing symptoms should always be reviewed sooner rather than waiting for the next planned test.
Related tests, treatments or support
A colonoscopy may be combined with other tests depending on your symptoms — for example blood tests, stool tests, a gastroscopy (camera test of the upper gut), or a CT scan. If a colonoscopy is incomplete, a CT colonography or capsule test may be used to see the rest of the bowel. Your team should explain how the tests fit together.
Follow-up & long-term care
Camera findings are often discussed on the day, but you should be told clearly how and when you will receive any biopsy results — usually within a couple of weeks — and who will explain them. Follow-up may include treatment, a planned repeat test, entry into a surveillance programme, or referral to a specialist. Chase your results if you have not heard within the expected time.
- Attend any planned surveillance colonoscopies at the interval your team recommends.
- Take part in NHS bowel cancer screening (the home FIT test) when invited, even after a normal colonoscopy.
- Report new or changing bowel symptoms promptly rather than waiting for the next scheduled test.
Repeat, follow-on and what comes next
- An incomplete or poorly prepared test may need to be repeated or followed by CT colonography.
- Large or multiple polyps sometimes need a further planned procedure to remove them safely.
- Surveillance colonoscopies are often planned at set intervals for higher-risk people.
- Ongoing or new symptoms after a normal test should be reviewed rather than assumed to be nothing.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- Clear written instructions and a named contact or unit number for problems at home.
- Specific warning signs explained (severe pain, heavy bleeding, fever) with what to do.
- A defined process and timeframe for biopsy results, with someone to explain them.
- A clear plan for any treatment, repeat test or surveillance interval.
- Advice to seek review if symptoms continue despite a normal result.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- The endoscopist's fee and the endoscopy unit/facility fee
- Whether sedation is used and the level of monitoring needed
- Whether polyps are removed or biopsies taken (polypectomy and pathology add cost)
- Laboratory fees for examining any samples
- Same-day reporting of camera findings versus standard turnaround for biopsies
- Any follow-up consultation to explain results and plan next steps
- Whether a repeat or alternative test is needed if the examination is incomplete
- The endoscopist's fee and the unit/facility fee
- Sedation and monitoring costs
- The cost of removing polyps and of laboratory analysis of any samples
- Whether a consultation to explain results is included
- The expected time for biopsy results and who will give them
- What happens (and what it costs) if the test is incomplete or needs repeating
- What happens, and who is responsible, if a complication occurs
- The cancellation and rebooking policy
On the NHS? Colonoscopy is widely available on the NHS for symptoms, screening and surveillance when clinically indicated; private access is mainly used for speed or choice and usually still needs a referral.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Not explaining the small but real risks of perforation and bleeding, especially with polyp removal.
- Not discussing sedation options, their risks, and the 24-hour driving and escort rules.
- Implying the test is 100% accurate, when polyps can be missed and the test can be incomplete.
- No clear plan for who gives the biopsy results and by when.
- No written aftercare advice or emergency contact for problems at home.
Marketing red flags
- Describing colonoscopy as 'risk-free' or 'usually not painful' without mentioning real risks.
- Guaranteeing that all polyps or cancers will be found.
- Pushing private colonoscopy without first considering whether a FIT test or other approach is appropriate.
- No information on the unit's completion or detection rates.
- No clear arrangement for managing a complication out of hours.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- Do I definitely need a colonoscopy, or would a different test answer the question?
- What are my sedation options, and what do you recommend for me?
- How should I manage my blood thinners or diabetes medicines beforehand?
- What is your unit's completion (caecal intubation) and polyp detection rate?
- What happens if you find and remove a polyp, and how does that change my risks?
- When and how will I get my biopsy results, and who will explain them?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my procedure, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this procedure not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Can I have a colonoscopy on the NHS?
Who is offered NHS bowel cancer screening, and how does it lead to a colonoscopy?
Is a colonoscopy painful?
Why is the bowel preparation so important?
Can a colonoscopy miss something?
When will I get my results?
What are the chances of a serious complication?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NHS — Colonoscopy British Society of Gastroenterology — endoscopy guidelines BSG / JAG — UK key performance indicators and quality standards for colonoscopy NHS — Bowel cancer screening BSG guidelines on sedation in gastrointestinal endoscopy (2023) GOV.UK — NHS bowel cancer screening programme overview (England) NHS inform — Bowel screening (Scotland) Public Health Wales — Bowel screening (Wales) nidirect — Bowel cancer screening (Northern Ireland)
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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