Key points
- In Spain, bowel cancer screening starts at 50 with a faecal occult blood test every 2 years, up to the age of 69.1
- A positive test does not mean cancer, but colonoscopy should not be delayed: waiting more than 9-10 months was associated with more cancers and more advanced stages.3
- In people at average risk, being invited to faecal testing is no worse than being invited to colonoscopy at reducing deaths from bowel cancer.2
- If the colonoscopy is normal, the next one is usually due after 10 years; if polyps are found, the interval depends on how many and what type.4
- With a family history the plan changes, and guidelines do not agree on everything: it is worth reviewing case by case.1,6
This article summarises the evidence and clinical guidelines so you can understand your situation. It does not replace an individual assessment.
“At what age should I have my first colonoscopy?” is one of the questions I am asked most, and the answer depends mainly on two things: your family history and whether or not you have symptoms.
The reason it is worth getting right is that most bowel cancers start as a benign polyp that takes years to become malignant. If the polyp is found and removed, the cancer never develops. It is not just early detection: it is prevention in the strict sense.
No family history and no symptoms
In Spain, the population screening programme invites people aged 50 to 69 to take a faecal occult blood test (faecal immunochemical test, or FIT) every two years. It is a simple test, with no preparation, done at home.1
If the test is negative, it is repeated after two years. If it is positive, a colonoscopy follows.
In the United States, given the rise in bowel cancer among younger people, the recommendation was brought forward in 2021 to 45.5 In Spain, the programme still starts at 50.
| Situation | Test | From | How often |
|---|---|---|---|
| Average risk (no family history) | Faecal occult blood test | Age 50 (Spanish programme) | Every 2 years, up to 69 |
| Positive faecal occult blood test | Colonoscopy | As soon as possible | Depending on the result |
| Normal colonoscopy at average risk | Repeat colonoscopy or return to screening | — | After 10 years |
| Warning symptoms | Diagnostic colonoscopy | At any age | This is not screening: investigate now |
If the faecal occult blood test is positive
This is the moment that causes most anxiety, and it helps to put it in context: in most cases no cancer is found, but rather polyps or benign causes such as haemorrhoids. It does mean a colonoscopy is needed, and that it should not be put off.
A study of more than 70,000 people with a positive test found that delaying colonoscopy up to 9 months did not increase risk, but from 10 months onwards the risk of cancer rose and, above all, of finding it at a more advanced stage.3
Do not repeat it to confirm
Repeating the faecal occult blood test after a positive result does not rule anything out. A positive result needs a colonoscopy even if the next test is negative.
Faecal test or straight to colonoscopy?
Colonoscopy is more sensitive but more invasive. The faecal test is simple and repeated every two years. The question of which is better has largely been answered by a large Spanish trial, COLONPREV, which invited more than 57,000 people aged 50 to 69 to colonoscopy or to faecal testing every two years. At ten years, inviting people to faecal testing was not inferior to inviting them to colonoscopy in terms of bowel cancer deaths.2
In practice: if you are at average risk, the programme’s test is an excellent option. If you would rather go straight to colonoscopy, that is a valid alternative. The worst option is doing neither.
With a family history
Here the starting age changes, and this is the point that raises most questions, not least because guidelines do not say exactly the same thing.
- One first-degree relative (parent, sibling or child) with bowel cancer increases risk by 1.4 to 1.9 times, less than many people fear.6 In this case the 2018 Spanish guideline suggests, once a hereditary syndrome has been ruled out, population screening with the faecal test.1 The US guideline, by contrast, proposes colonoscopy every 5 years from 40 if that relative was diagnosed before 60.7
- Two or more first-degree relatives: colonoscopy, usually from age 40 or 10 years before the youngest case, and every 5 years if normal.1,7
- Cancer in a very young relative, several cases in successive generations or endometrial cancers in the same family: a hereditary syndrome such as Lynch syndrome must be ruled out, as it has its own schedule.1
- Grandparents, uncles, aunts or cousins on their own almost never change the starting age.
That is why, when there is a family history, it is worth going through the family tree carefully: who, exactly what type of cancer and at what age.
How often to repeat colonoscopy
It depends on the result, and there is no fixed interval for everyone. The 2020 European guideline greatly simplified surveillance:4
| Colonoscopy result | Next step |
|---|---|
| Normal, at average risk | Repeat colonoscopy or return to screening after 10 years |
| 1 to 4 adenomas under 10 mm without high-grade dysplasia | No specific surveillance: return to screening after 10 years |
| 5 or more adenomas, any of 10 mm or more, or with high-grade dysplasia | Colonoscopy after 3 years |
| Serrated polyp of 10 mm or more, or with dysplasia | Colonoscopy after 3 years |
| Polyp of 20 mm or more removed in pieces | Check of the site after 3-6 months |
Leave with a date
Leaving a colonoscopy without knowing when the next one is due is a very common loose end. That interval should be written in the report once the pathology result is known.
About the bowel preparation, which worries people most
Almost all patients agree that the uncomfortable part is not the test, which is done under sedation, but the bowel cleansing the day before.
It is worth doing it well: a colonoscopy is only as good as its preparation, and inadequate cleansing may mean repeating it or missing a polyp. Lower-volume, better-tolerated preparations are now available, and splitting the dose between the evening before and the morning of the test improves the result. If you have had a bad experience before, say so in advance and an alternative can be found.
Common myths
“If I have no symptoms, I don’t need it.”
Screening is precisely for people without symptoms: it finds polyps before they turn into cancer.
“If the test is positive, I have cancer.”
In most cases polyps or benign causes are found. But a positive result always needs a colonoscopy.3
“If it is positive, I will repeat it to make sure.”
Repeating the test rules nothing out. A positive result needs a colonoscopy even if the next test is negative.
“Colonoscopy is painful.”
It is done under sedation, and most patients do not remember it. The hardest part is the preparation.
“After a normal colonoscopy it needs repeating every year.”
At average risk, after a normal, good-quality colonoscopy, the next one is due after 10 years.4
“My grandfather had bowel cancer, so I should start at 40.”
Second-degree relatives on their own almost never change the starting age. First-degree relatives are what count.1
Warning signs: do not wait
Do not wait for screening age if you have…
Everything above is for people without symptoms. If you have any of the following, the bowel needs investigating now, whatever your age:
- Blood in the stools or black stools
- A change in bowel habit lasting more than a few weeks
- Anaemia or iron deficiency without a clear cause
- Unintentional weight loss
- Persistent abdominal pain or a feeling of incomplete emptying
How I approach it in clinic
I review your age, family history (who, which cancer and at what age), whether you have had symptoms and, if you have already had colonoscopies, their reports and pathology results. With that we decide which test is right for you and when.
When colonoscopy is indicated, I perform it under sedation, prescribe a low-volume preparation and give you a report with the date of the next check, once the polyp results are known.
Not sure when to start or how often to repeat?
We review it with your history and family background in front of us, and you leave with a plan and a date.
Frequently asked questions
I am 45 with no family history. Should I have a colonoscopy?
In Spain screening starts at 50. In the United States it is recommended from 45, because of the rise in bowel cancer among younger people.5 If you are unsure or have symptoms, it is sensible to discuss it in clinic.
Which is better, the faecal test or colonoscopy?
At average risk both are valid: in the COLONPREV trial, inviting people to faecal testing was not inferior to inviting them to colonoscopy for deaths at 10 years.2 What matters is doing one of them.
I had polyps removed. When is my next one due?
It depends on the number, size and pathology result. With 1 to 4 small adenomas, most people need no special surveillance; with larger or more numerous polyps, after 3 years.4
How long do polyp results take?
The pathology report usually takes one to three weeks. The date of the next colonoscopy is set once it is available.
References
- Cubiella J, et al. Clinical practice guideline. Diagnosis and prevention of colorectal cancer. 2018 update. Gastroenterol Hepatol. 2018. PubMed
- Castells A, et al. Effect of invitation to colonoscopy versus faecal immunochemical test screening on colorectal cancer mortality (COLONPREV): a pragmatic, randomised, controlled, non-inferiority trial. Lancet. 2025. The Lancet
- Corley DA, et al. Association between time to colonoscopy after a positive fecal test result and risk of colorectal cancer and cancer stage at diagnosis. JAMA. 2017. PubMed
- Hassan C, et al. Post-polypectomy colonoscopy surveillance: European Society of Gastrointestinal Endoscopy (ESGE) Guideline – Update 2020. Endoscopy. 2020. Full text
- US Preventive Services Task Force; Davidson KW, et al. Screening for colorectal cancer: US Preventive Services Task Force recommendation statement. JAMA. 2021. PubMed
- Roos VH, et al. Effects of family history on relative and absolute risks for colorectal cancer: a systematic review and meta-analysis. Clin Gastroenterol Hepatol. 2019. PubMed
- Rex DK, et al. Colorectal cancer screening: recommendations for physicians and patients from the U.S. Multi-Society Task Force on Colorectal Cancer. Am J Gastroenterol. 2017. PubMed
Links go to PubMed or the original publication and open in a new tab.
Related reading
Dr Fernando Casals Seoane
Consultant gastroenterologist with a PhD in Medicine from the Autonomous University of Madrid. He has worked at La Princesa University Hospital since 2009 and sees private patients at Ruber Juan Bravo Hospital. Certified by the European Board of Gastroenterology and Hepatology and honorary lecturer at the UAM. Principal investigator in international clinical trials on acute pancreatitis, including WATERFALL (NEJM, 2022).
Transparency: this article is not sponsored and does not promote any product or brand. All sources are linked.