Why surveillance colonoscopies come on a schedule

If your inflammatory bowel disease affects the colon or rectum, at some point the appointments start to include a colonoscopy that has nothing to do with how you feel. Nothing has flared. The purpose is surveillance: looking at the lining for changes before they become something. The British Society of Gastroenterology published updated guidelines on this in Gut in 2025, and the structure is worth understanding, because it explains why two people with the same diagnosis are given very different intervals.

When it starts

The guidelines say that people with inflammatory bowel disease affecting the colon or rectum should be risk assessed for entry into a surveillance programme starting eight years after the onset of their symptoms. Not eight years after the diagnosis — after the symptoms began, which for many people is a meaningfully earlier date. There is one group that does not wait at all: people whose colitis is associated with primary sclerosing cholangitis are to be offered surveillance from the time of diagnosis.

Four tiers, not one interval

Rather than a single schedule, the guidelines sort people into four tiers by their calculated five-year risk of advanced colorectal neoplasia. Each tier carries its own answer:

1. Large risk: the guidance is to consider colectomy. This tier covers severe active inflammation that has not settled despite optimised medical treatment, along with anyone whose calculated risk falls in this band.
2. Moderate risk: surveillance every year. Moderate active inflammation, a history of dysplasia, primary sclerosing cholangitis, or a stricture in the colon place someone here.
3. Small risk: surveillance every three years. Mild active inflammation or extensive disease sits at this level.
4. Close to population risk: every ten years, alongside ordinary population screening.

The top tier is the one that surprises people, because its answer is not an interval at all. Where the risk is high enough, the guidance is that surgery is the thing to discuss rather than a shorter gap between cameras.

What moves someone between tiers

The factors the guidelines use to place someone are:

• how severe the inflammation is, and whether it is still active
• whether primary sclerosing cholangitis is present
• a history of dysplasia
• strictures in the colon
• post-inflammatory polyps
• how much of the bowel the disease affects

Two of those are worth pausing on, because they are not fixed. Inflammation is treatable, and the extent of disease is reassessed at each look. A tier is a description of where things stood at the last assessment rather than a permanent category, which is why an interval can change.

Why the liver condition changes the timing

Primary sclerosing cholangitis is a disease of the bile ducts that occurs alongside colitis far more often than chance would explain, and it shifts the risk sharply. The guidelines cite a cohort that estimated the risk of colorectal cancer or dysplasia in this group at 9 per cent within the first ten years, which is the reasoning behind starting surveillance immediately rather than waiting the usual eight years.

None of this is a schedule anyone can set for themselves. The tiers depend on findings from the last colonoscopy and on how active the inflammation has been, which is information your team holds and you may not. What it does explain is why the interval you have been given may not match someone else’s with the same diagnosis, and why it is a number that can move.