Colonoscopy and Bowel Cancer Screening

Bowel (colorectal) cancer is one of the commonest cancers — and one of the most preventable.
Most bowel cancers develop slowly, over years, from small growths called polyps on the lining of the bowel. A polyp is not a cancer, but a small number of polyps gradually change.
Screening means looking for polyps or early cancer in people who feel completely well — removing polyps before they ever become cancer, and finding cancers at a stage when they are usually curable.

That is the whole point of this guide: screening is for people with no symptoms. Symptoms are a different matter, and are covered — clearly — below.

• Average risk: screening is recommended for all adults from the age of 45 — this is the standard advice of major international guidelines (including the US Preventive Services Task Force and the American Cancer Society)
• It continues, for most people in good health, until about the age of 75; after that it is individualised
• Family history: if a close relative (parent, sibling or child) had bowel cancer — especially before the age of 60 — or had advanced polyps, screening should start earlier: usually at 40, or 10 years younger than the age at which your relative was diagnosed, whichever comes first, and it is usually done by colonoscopy
• Higher risk still: people with inflammatory bowel disease (ulcerative colitis or Crohn's disease of the colon), or inherited conditions such as Lynch syndrome, need a specialist programme that starts younger — ask your surgeon or gastroenterologist

1. The stool test (FIT)

• A small sample of stool is tested at home for invisible traces of blood (the faecal immunochemical test — FIT)
• If repeated on schedule (usually every year), it is a good screening tool
• A positive FIT does not mean cancer — it means a colonoscopy is needed to find the source of the blood
• Its limitation: it cannot remove anything, and small polyps that do not bleed can be missed

2. Colonoscopy

• A thin, flexible camera is passed through the back passage to inspect the whole large bowel directly
• It is the most complete test: it sees the polyps, and removes them during the same procedure
• If a colonoscopy is normal, the next one is usually not needed for about 10 years in an average-risk person
• It requires a day of preparation (below) and sedation, and carries small risks (below)

For many average-risk people a reasonable approach is a yearly FIT, with colonoscopy whenever the FIT is positive or whenever symptoms appear. Others prefer the certainty of a colonoscopy at 45 and then every 10 years. Both are legitimate — discuss which fits you.

If you have any of the following, do not book a screening test and wait. Book a medical appointment promptly — these symptoms deserve investigation at any age, even in your twenties and thirties:

• Bleeding from the back passage, or blood in the stool — never assume it is “just piles” without assessment
• A persistent change in bowel habit (looser stools, or new constipation) lasting more than a few weeks
• Unexplained iron-deficiency anaemia, or unusual tiredness with pallor
• Losing weight without trying
• A lump that can be felt in the tummy
• Persistent abdominal pain or bloating that is new for you

• You will usually have sedation through a drip — most patients are drowsy and comfortable, and remember little
• The test takes about 20–45 minutes. Air or carbon dioxide is used to open the bowel for a clear view; mild bloating afterwards is normal
• If polyps are found, they are usually removed there and then (polypectomy) with a wire loop — you feel nothing — and sent to the laboratory
• Small tissue samples (biopsies) may be taken from anything that needs checking
• You recover in the unit for an hour or two and go home the same day — with an adult to accompany you, because of the sedation. Do not drive that day

• You will be told the findings the same day, and whether polyps were removed
• Laboratory results on polyps take some days; your follow-up plan — discharge, or a repeat colonoscopy in a set number of years — depends on the number, size and type of polyps found
• Mild bloating and wind pass quickly; you can usually eat normally the same evening and work the next day

I feel perfectly well. Why should I have this done?

Because polyps and early bowel cancers cause no symptoms — that is precisely when they are easiest and safest to deal with. Waiting for symptoms means waiting for a later stage.

Is colonoscopy painful?

With sedation, most patients are comfortable and remember little of the test itself. The preparation the day before is honestly the harder part — and it is one day, for years of protection.

What if a polyp is found?

Then the screening has done its job. Most polyps are benign and are removed during the same procedure. The laboratory type decides your surveillance interval — anything from “no further tests for 10 years” to a repeat in 1–3 years.

Of all the tests in this guide series, screening colonoscopy is the one that can prevent a cancer rather than merely find one.
If you are 45 or over and have never been screened — or have a family history and have never discussed it — bring it up at your next visit.
One uncomfortable day of preparation, in exchange for finding and removing the problem years before it could have harmed you, is a trade worth making.