Colonoscopy

A colonoscopy examines the whole of the large bowel (colon and rectum). A thin, flexible tube with a camera at its tip is passed through the back passage and guided all the way round the colon. It is usually done as a day procedure under sedation. Polyps found can usually be removed in the same session.

Why it is done

• Screening for colorectal cancer, one of the most common cancers in Singapore. See colorectal cancer screening.
• Blood in the stool, a positive stool test (FIT), or anaemia
• A lasting change in bowel habit, or abdominal pain
• Unexplained weight loss
• Follow-up after polyps have been removed, or for inflammatory bowel disease

Bowel preparation: why it matters

A colonoscopy is only as good as the view. If stool or cloudy fluid is left in the bowel, polyps, especially small and flat ones, can be hidden. A well-prepared bowel is one of the most important things you can do to make your colonoscopy worthwhile.

• More polyps foundA clean lining lets small and flat polyps be seen and removed before they can turn into cancer.
• Fewer repeat testsIf the preparation is poor, the colonoscopy may need to be repeated, or repeated sooner than usual.
• A safer, smoother procedureA clear view makes it easier to reach the start of the colon and to remove polyps.

Quality standards expect the bowel preparation to be adequate in at least 90% of colonoscopies. Most of that depends on following the instructions carefully at home.

How to prepare

• Two days before: a low-fibre diet. Avoid fruit, vegetables, beans, seeds, nuts and whole grains. White rice, porridge, white bread, noodles, eggs, fish, meat and tofu are usually fine.
• The day before: a light dinner at 5 to 6pm, then the first dose of bowel preparation. After that, clear fluids only, such as water, clear soup, clear apple juice, tea or coffee without milk, and isotonic drinks. Avoid red or purple drinks.
• The bowel-cleansing drink: usually split into two doses, one the evening before and one about 5 hours before the procedure. Splitting the dose gives a cleaner bowel than taking it all the night before.
• When you are ready: your stools should be clear or light yellow liquid, without solid bits. If they are still brown or murky, tell the clinic.
• Medicines: tell the clinic about blood thinners, diabetes medicines, iron tablets and allergies. Some need to be adjusted or paused, and iron tablets are usually stopped a week before.

People who are often constipated, have diabetes, or have had a poor preparation before may need a longer or stronger preparation. Mention this when the colonoscopy is booked. Always follow the instructions your clinic gives you, as timings can differ.

Print the colonoscopy preparation sheet to fill in your times.

During the procedure

With sedation, most people sleep lightly through the procedure. The scope is passed to the start of the colon (the caecum), and the lining is then examined carefully as the scope is slowly withdrawn. Polyps are usually removed with a small wire loop and sent to the laboratory. The procedure usually takes about 20 to 45 minutes, depending on what is found. What a complete colonoscopy should include is explained in the colorectal cancer screening guide.

After the procedure

You rest for a short while as the sedation wears off, and Dr Chia explains what was seen. Some bloating or wind is common and settles within hours. You should not drive, operate machinery or sign important documents for the rest of the day, and it helps to have someone accompany you home. Laboratory results for polyps or biopsies usually take a few days, and decide when your next colonoscopy is due.

Is it safe?

Colonoscopy is a common and generally safe procedure. The main risks are bleeding after polyp removal, which is usually minor, and a tear in the bowel wall (perforation), which is rare, in the order of 1 in 1,000 procedures or fewer. Seek medical attention promptly for severe abdominal pain, fever, or heavy bleeding after the procedure, including in the days after a polyp is removed.

A gastroscopy and a colonoscopy can be done in the same session, under one sedation. Dr Chia will advise whether you need one or both.

Insurance

Dr Chia is on the specialist panels of AIA, Great Eastern, HSBC Life, Income, Prudential, Raffles Shield and Singlife for Integrated Shield Plans, and on many corporate insurance panels (see all panels). Check your coverage with your insurer.

General information only. Reviewed by Dr Chia Chung King, 2026-11-07. Book a consultation.