Surveillance colonoscopy: when the next one is due

Surveillance is not screening

Screening is for people with no symptoms and nothing previously found. Surveillance is what happens afterwards, once something has been found and removed, because having had one polyp makes another more likely.

The purpose is worth being clear about. Repeating a colonoscopy is about finding and removing new polyps before any of them turns into a cancer. It is prevention rather than detection, and that is why the intervals are measured in years rather than months. Adenomas take a long time to become anything.

Start with your own report

The four things that decide it

• How many polyps were removed. The count matters more than anything else.
• How big the largest one was. Ten millimetres is the line that changes most recommendations.
• What type they were. Conventional adenomas, serrated lesions and hyperplastic polyps behave differently. Small hyperplastic polyps in the rectum and lower colon carry no meaningful risk and do not shorten the interval.
• What the pathologist saw down the microscope. Villous features and high-grade dysplasia both bring the next colonoscopy forward.

A fifth factor sits underneath all of them, and it has its own section below: how good a look the camera actually got.

If conventional adenomas were removed

These are the figures in the Australian guideline. The guideline itself runs to more permutations than are useful here, so this is the common ground.

• 1 or 2 small adenomas (under 10 mm), tubular, no high-grade dysplasia5 to 10 years
• 1 or 2 adenomas under 10 mm, but villous or with high-grade dysplasia3 years
• 3 or 4 tubular adenomas, all under 10 mm, no high-grade dysplasia5 years
• 1 or 2 adenomas of 10 mm or more3 years
• 3 or 4 adenomas where any is 10 mm or more3 years
• 5 to 9 adenomas, all small and tubular3 years
• 5 to 9 adenomas, any of them 10 mm or more, villous or with high-grade dysplasia1 year
• 10 or more adenomas1 year

Two notes on the first row. The guideline's evidence-based recommendation is that surveillance should be no sooner than five years after low-risk adenomas only, and its consensus is that ten years suits most people with one or two small tubular adenomas. Five years is what is commonly used in Australian practice. Where the adenomas were tiny, under 6 mm, returning to the national screening program after four years is also reasonable.

Ten or more adenomas prompts a look for a genetic cause as well as a one year interval.

A note on the second row, because the guidelines disagree here and it is worth knowing which one you are being given. A single adenoma under 10 mm containing high-grade dysplasia, completely removed and with nothing else found, sits at five years under the Australian guideline and at three years under both the American and the European ones. The British guideline does not offer surveillance for it at all. A/Prof Kariyawasam uses three years for this finding, which is the interval most of the world has settled on, and the shorter interval assumes the polyp was removed in its entirety. Where complete removal is not certain, an earlier look may be needed instead.

If you are also having colonoscopies because of a family history, the two schedules are compared and the shorter one is used. Where a genetic syndrome is known or suspected, that takes over entirely and the intervals come from a different guideline.

If serrated lesions were removed

Serrated lesions are flat, pale and covered in mucus, which makes them easier to miss than a conventional adenoma. They matter because a proportion of bowel cancers arise through them, and because they are rising fastest in younger patients. Older reports may call them sessile serrated adenomas.

• 1 or 2 sessile serrated lesions under 10 mm, no dysplasia5 years
• 3 or 4 sessile serrated lesions under 10 mm, no dysplasia3 years
• 1 or 2 sessile serrated lesions of 10 mm or more, or with dysplasia3 years
• 1 or 2 traditional serrated adenomas3 years
• 5 or more sessile serrated lesions1 year
• 3 or 4 sessile serrated lesions of 10 mm or more, or with dysplasia1 year
• 3 or 4 traditional serrated adenomas1 year

Where both serrated lesions and conventional adenomas were found, they are counted together and the shorter of the two intervals applies.

How Australia compares with the rest of the world

Guidelines in different countries read much the same evidence and land in different places. It is worth knowing, because a number found online often will not match the one on your letter.

Scroll the table sideways to see all four. Sources for each are listed at the foot of this page.

Where they agree is at the serious end. An adenoma of 10 mm or more, high-grade dysplasia or five or more adenomas brings a three-year interval in Australia, the United States, Europe and the United Kingdom alike.

They differ after one to four small adenomas. The United Kingdom and Europe return most of that group to the national screening program without a surveillance colonoscopy. The United States suggests seven to ten years. The Australian guideline sets five years as the earliest and suggests ten for most.

The gap has less to do with the evidence than with what each country has around it. Where a national screening program is well established and well attended, returning someone to it is a reasonable substitute for a colonoscopy. A five-year interval, which is what many patients here are given, sits at the shorter end of that international range and inside what the Australian guideline allows.

If a large polyp was removed in pieces

A large or flat lesion taken out by endoscopic mucosal resection is followed up differently, and sooner, because a small amount of tissue can be left behind at the edges.

• Removed in one piece: a check at about 12 months
• Removed piecemeal: a check at about 6 months

At that check the scar is found, photographed and examined systematically, with biopsies taken, because recurrence at the scar is the thing being looked for and it is not always visible.

After a bowel cancer has been removed

This is a separate schedule and it starts sooner.

• A colonoscopy one year after the operation, unless a complete one was done shortly after surgery
• If that is clear, the next at six years, then at eleven years
• If all three are clear, follow-up can continue with either a faecal occult blood test every two years or a colonoscopy at ten years

If an advanced adenoma is found at any of them, the schedule reverts to the adenoma intervals above.

Surveillance in inflammatory bowel disease

Long-standing colitis carries its own risk, and surveillance here is about looking for changes in the lining rather than counting polyps.

When it starts

• Eight years after symptoms started, for anyone with at least left-sided ulcerative colitis, or Crohn's colitis involving at least a third of the colon.
• At the time primary sclerosing cholangitis is diagnosed, for anyone who has it, regardless of how long the colitis has been present.
• Where a first-degree relative has had bowel cancer, it can begin at eight years from symptom onset or ten years before the age that relative was diagnosed, whichever comes first.
• Disease confined to the rectum, and Crohn's disease affecting only the small bowel, do not need this surveillance at all.

How often, once it has started

• Yearly with any of: primary sclerosing cholangitis, ongoing active inflammation, dysplasia found previously, a stricture, pseudopolyps or a shortened tube-like colon, or a first-degree relative who had bowel cancer at 50 or under.
• Every three years where the disease is quiet and none of those apply.
• Every five years where the disease is quiet, nothing on that list applies and consecutive examinations have both been clear. This is a step down from three years once that track record exists, rather than a separate starting point.

Chromoendoscopy, which uses a dye sprayed on the lining to make subtle changes visible, is recommended for these examinations, and biopsies are aimed at what can be seen rather than taken at random.

There is more on the inflammatory bowel disease page.

Why two people with the same polyps get different dates

Every interval on this page assumes the colonoscopy saw the whole bowel properly. Two things change that, and both are in the report.

• The bowel preparation. If the clean-out was poor, polyps were probably missed, and the sensible response is to repeat the examination sooner rather than to schedule the next one years away on findings that cannot be trusted.
• Whether the caecum was reached. An examination that did not get to the far end of the colon has not looked at all of it.

Both are fair things to ask about, and they explain a good proportion of the differences between one person's date and another's.

When surveillance stops

Surveillance does not go on indefinitely, and working out when to stop is one of the harder conversations in this area. It is not a birthday. Age on its own says very little about whether another colonoscopy will help, and two people of the same age can sit in completely different places.

What the decision actually rests on:

• What the previous colonoscopies found, and how long ago. Someone whose last two were clear is in a different position from someone who has had large or repeated adenomas.
• General health and physical fitness, which carry more weight than the number of years.
• Other medical conditions, and how they would bear on both the bowel preparation and the sedation. The preparation is often the harder part.
• What the person wants, once they understand what is being weighed.

The principle underneath is simple even when the decision is not. A polyp removed today only helps someone who has the years ahead for it to have mattered. The British guideline puts it as a life expectancy of more than ten years. Over time the chance of finding something that changes anything falls, while the demands of the preparation and the risks of the procedure rise. At some point the two cross. Where that point sits is different for every person, and guidelines offer age brackets only as a prompt to have the conversation, not as a line to be applied.

It is worth raising rather than waiting for a letter that does not arrive.

Where surveillance colonoscopy is arranged in Sydney

A/Prof Viraj Kariyawasam is a consultant gastroenterologist and hepatologist, recertified in adult colonoscopy. Surveillance intervals and overdue recalls are reviewed at consultation in Norwest, Rouse Hill, Pennant Hills and Macquarie Park.

The colonoscopy itself is performed at Norwest Private Hospital, Macquarie University Hospital and Pennant Hills Day Surgery. A referral from your GP is needed for a consultation.