When should you have your first colonoscopy?

“When should I have my first colonoscopy?” is one of the most productive questions a patient can bring to clinic. Colorectal cancer is among the most common cancers in Singapore, in both men and women — and, unusually for a cancer, it is largely preventable, because most cases grow slowly from polyps that can be found and removed years before they become dangerous.

The short answer, for most people, is that screening starts at fifty. The longer answer depends on your family history, your symptoms, and a few situations that move the timeline forward.

Why fifty is the screening age

Most colorectal cancers begin as polyps — small growths on the lining of the large intestine that are harmless when they first form. A polyp typically takes years, often a decade or more, to change into a cancer, and for nearly all of that time it causes no symptoms whatsoever.

That long, silent runway is what screening exploits. Singapore’s Ministry of Health recommends that people at average risk — no symptoms, no family history of colorectal cancer, no conditions such as inflammatory bowel disease — begin screening at age 50, with either a FIT stool test every year or a screening colonoscopy.

“Average risk” is doing real work in that sentence. If anything in the next section applies to you, fifty may already be too late a start.

When your first colonoscopy should come earlier

I bring the timeline forward in several situations:

• A family history of colorectal cancer. If a parent, sibling or child has had the disease, screening should begin ten years before the age at which they were diagnosed — a father diagnosed at 55 means his children start at 45.
• Symptoms, at any age. Rectal bleeding, a persistent change in bowel habit — stools that have become looser, harder or narrower, or a new sense of incomplete emptying — unexplained weight loss, or abdominal discomfort that will not settle. These call for a diagnostic colonoscopy now, not a screening schedule later.
• Iron deficiency anaemia. Low iron without an obvious cause can be the only sign of slow, invisible bleeding from the bowel. It should be investigated, not simply topped up with iron tablets.
• A positive FIT result. A stool test that finds hidden blood has done its job — the next step is a colonoscopy to find out where the blood is coming from.
• Inflammatory bowel disease and certain inherited bowel conditions, which need earlier and more frequent surveillance, planned individually.

What a colonoscopy involves — and why it prevents cancer

A colonoscopy examines the entire large intestine using a flexible camera passed through the rectum. It is done under sedation — most patients sleep through it — takes roughly 15 to 30 minutes, and is a day procedure, which I perform at MOH-accredited day surgery and endoscopy centres. The day before, you take a bowel preparation to empty the colon so the lining can be seen clearly.

What makes colonoscopy different from almost every other screening test is that it treats as it looks. A polyp found during the examination is removed in the same sitting, and a removed polyp can never become a cancer. That is why colonoscopy both detects cancer and prevents it. If the examination is normal and your risk is average, it typically does not need repeating for ten years; if polyps are found, the interval shortens to around three to five.

FIT or colonoscopy — a fair comparison

The FIT (faecal immunochemical test) checks a small stool sample for microscopic traces of blood. Its strengths are real: it is done at home, needs no preparation or sedation, and costs little. Its limits are equally real: it detects bleeding rather than polyps, so a polyp that happens not to be bleeding can be missed — which is why FIT only works as a yearly habit, not a one-off — and a positive result still leads to a colonoscopy to find the cause.

Colonoscopy asks more of you on the day — the preparation, the sedation, time off — and, like any procedure, it carries small risks, which I discuss beforehand. In return it examines the bowel directly, removes what it finds, and buys years between tests.

I put it to patients plainly: the screening test that helps you is the one you actually do. An annual FIT faithfully done is far more useful than a colonoscopy endlessly postponed — and colonoscopy is the definitive examination whenever anything needs a closer look.

When not to wait

If you are fifty or older and have never been screened, the practical advice is simple: start now, with whichever test you will follow through on. And at any age, bleeding from the back passage, a change in bowel habit that persists beyond a couple of weeks, unexplained weight loss or unexplained anaemia deserve prompt assessment rather than observation. Bleeding is easy to blame on haemorrhoids — sometimes correctly — but that is a diagnosis to confirm after examination, not to assume. These assessments are part of my general surgical practice, and an early look is almost always a smaller undertaking than a late one.