Why this is prevention, not just diagnosis
Most bowel cancers arise from a benign polyp that takes years to turn malignant. That window of time is what sets it apart from other tumours: if the polyp is found and removed, the cancer never develops.
This is not early detection. It is prevention in the strict sense, and it is why doing it properly matters.
No family history or symptoms
In Spain, population screening begins at 50 with a faecal occult blood test every two years. It is a simple test, with no preparation, done at home.
If negative, it is repeated after two years. If positive, a colonoscopy follows.
A positive test does not mean cancer
In most cases a polyp or a benign cause such as haemorrhoids is found. What it does mean is that a colonoscopy is needed, and that it should not be put off.
With a family history
Here the starting age changes, and this is the point that causes most confusion.
- One first-degree relative (parent, sibling or child) with bowel cancer: start ten years before the age at which that person was diagnosed, and go straight to colonoscopy.
- Several affected relatives, or cases at a young age: the approach changes and genetic assessment is sometimes appropriate.
- Relatives with advanced polyps: this also alters the schedule, even without cancer.
A concrete example: if your father was diagnosed at 55, you would start at 45.
Situations that bring investigation forward
Regardless of age, some symptoms require the bowel to be investigated without waiting for screening:
- Blood in the stool
- A sustained change in bowel habit over weeks
- Iron deficiency anaemia with no clear cause
- Unintentional weight loss
- Persistent abdominal pain
How often to repeat it
It depends on the result, and the interval is not the same for everyone.
If the colonoscopy is normal and there is no family history, the interval is usually long, up to ten years. If polyps are found, it shortens according to how many there are, their size and their characteristics under the microscope.
Leave with the date
Leaving a colonoscopy without knowing when the next one is due is a very common loose end. That interval should be set out in writing in the report, once the pathology result is known.
About the preparation, which worries people most
Almost all patients agree that the uncomfortable part is not the procedure, which is done under sedation, but the bowel cleansing the day before.
It is worth doing properly: a colonoscopy is only as good as the cleansing, and inadequate preparation may mean repeating it. Lower-volume, better-tolerated preparations now exist, so if you have had a bad experience before, say so beforehand and an alternative will be found.
If you are unsure when to start or how often to repeat, it is worth reviewing it with your history and family background to hand.