Preparing for a colonoscopy
Bowel preparation is the one part of a colonoscopy you control.
Here is what Dr Sulaiman's patients are asked to do before a colonoscopy: the low-fibre days, the clear liquid day, the split-dose laxative, and the medicines that need pausing first.
FRCSEd (General Surgery)10,000+ endoscopic procedures
His story
Dr Sulaiman Bin Yusof
Senior Consultant Colorectal and General Surgeon, seeing patients at five clinics in Singapore.
- MBChB (Sheffield), M.Med (Surgery), FRCSEd (General Surgery)
- Consults in English and Malay
- MOH Fellowship, Peter MacCallum Cancer Centre, Melbourne
- Singapore Health Quality Service Star Award 2023
- Dean's Honour Roll for Teaching
Why it matters
The scope can only see what the preparation clears.
A clean bowel is what makes the result accurate.
A colonoscopy looks for polyps, and a polyp can be a few millimetres across and flat against the bowel wall. Residue left behind hides exactly that. This is why the preparation is not administrative fuss around the procedure. It is the part of the procedure that decides how much of the bowel is genuinely examined.
Incomplete preparation limits what can be seen, and the honest answer when the view is poor is to repeat the examination rather than report a scope that could not see properly. That means another round of preparation, another day off, and a delay before you have an answer. Getting it right the first time is worth the evening it costs.
His team gives you written instructions at the pre-procedure consultation, covering the diet, the laxative and any medication changes your own history calls for. This page is what those instructions ask of you, set out in the order you will meet them. Where the two differ, follow the clinic’s letter.
The days before
Three days out, fibre comes off the plate.
Fibre is the part the laxative struggles to shift.
From three days before the procedure, move to a low-fibre diet. Nothing about this is a fast. You eat normally, in normal amounts, from a narrower list.
Eat freely
- White rice, white bread and refined pasta
- Eggs
- Fish and chicken
- Tofu
Leave out
- Wholegrains and high-fibre cereals
- Raw vegetables
- Fruit with seeds or skin
- Nuts and beans
For a fuller picture of what this looks like across a week of meals, read the low-residue diet article.
The day before
Clear liquids only, and nothing red or purple.
Clear means you can see through it, not that it has no colour.
Permitted
- Clear broths
- Water, plain tea and black coffee
- Clear fruit juices without pulp
- Isotonic sports drinks
Not permitted
- Any solid food
- Milk and dairy
- Anything red or purple in colour
Red and purple drinks are ruled out for a specific reason. Their colour looks like blood on the camera, and a stain that might be blood has to be treated as though it is.
On the day itself you continue with clear liquids only, up to the cutoff time the clinic gives you, and then take nothing by mouth, water included. That final cutoff is set by the anaesthetic requirement rather than by the preparation, so it comes from the clinic’s letter rather than from a website.
The laxative
Two doses, split across the evening and the morning.
The inconvenient version is the one that cleans better.
First dose, the evening before
Bowel movements usually begin within one to two hours and come in waves.
Second dose, early the next morning
Typically four to six hours before the scheduled procedure time.
Clear and pale
Stools become a clear or pale yellow liquid, close to the look of urine, with nothing solid and no cloudiness.
Why it is split at all
A single large dose the night before is easier to face and it does not clean as well. Splitting it is the joint recommendation of the American College of Gastroenterology, the American Gastroenterological Association and the American Society for Gastrointestinal Endoscopy (source: US Multi-Society Task Force on Colorectal Cancer, bowel preparation consensus recommendations (ACG, AGA and ASGE), opens in a new tab), and two separate meta-analyses of controlled trials reached the same conclusion, one in 2014 (source: Bucci C, et al. Optimal bowel cleansing for colonoscopy: split the dose. Gastrointestinal Endoscopy, 2014, opens in a new tab) and one in 2015 (source: Martel M, et al. Split-dose preparations are superior to day-before bowel cleansing regimens. Gastroenterology, 2015, opens in a new tab). It is also generally better tolerated than the single dose, which surprises most people who hear about it for the first time.
When it is taken on the day instead
In some cases the full dose is taken on the morning of the procedure rather than split. Whether that suits you depends mostly on when your colonoscopy is scheduled, and the clinic will tell you which version you are on. Do not switch between the two on your own.
If the preparation is not going to plan, tell the clinic that evening rather than discovering it in the endoscopy suite. There is usually something that can be done while you are still at home.
Medicines
Bring the whole list, including what you bought yourself.
Supplements and over-the-counter remedies count.
Some medicines need adjusting or pausing before a colonoscopy, either because they obscure the view or because they raise the bleeding risk if a polyp is removed during the same session. Tell him everything you take at the pre-procedure consultation, and he will tell you which of these apply to you.
Iron supplements
Stop at least five days before the procedure. Iron coats the bowel lining and darkens it, and that alone can be enough to spoil an otherwise good preparation.
Anti-diarrhoeal medicines
Loperamide and anything like it comes off before you start the bowel preparation, for the obvious reason that the two are working against each other.
Aspirin and anti-inflammatories
These may need to be paused, and whether they do depends on your dose and on why you are taking them. It is a question for the consultation rather than a rule that applies to everybody.
Blood thinners and diabetes medicines
Both need individual instructions, and both are set out in the next section. Neither should be changed on your own reading of a page.
Diabetes and blood thinners
Two situations that need instructions written for you.
He reviews these at the consultation and writes the plan down.
If you have diabetes
The preparation day is a day of clear liquids and significant fluid shifts, so the usual doses stop matching the usual intake. Metformin is generally withheld on the day of the procedure for that reason. Insulin doses often need reducing, both on the preparation day and on the day itself, and the size of that reduction is something his team advises rather than something you estimate.
Monitor your blood glucose through the preparation period. That is the part you can do that nobody else can, and it is what tells the team whether the plan is holding.
If you take blood thinners
Warfarin, aspirin, clopidogrel and the newer anticoagulants such as rivaroxaban and apixaban all raise the bleeding risk, and they matter most if a polyp is removed during the same session. You will be given specific instructions on when to pause and, just as importantly, when to restart.
Do not stop or adjust a blood thinner without guidance from him or from the doctor who prescribed it. The reason you are on it has not gone away because you have a colonoscopy booked, and the risk of stopping wrongly can be larger than the risk of the procedure.
Getting through it
The evening is more manageable than people expect.
Most of what makes it hard has a practical answer.
Chill it first
The solution is easier to drink cold. Put it in the fridge before you need it, not when you are already staring at it.
Sip through a straw
Steady sipping through a straw is better tolerated than gulping, and gulping is what brings the nausea on.
Keep a chaser to hand
Plain water or a clear isotonic drink between mouthfuls clears the taste and keeps you drinking.
Protect the skin
A barrier cream around the anus before you start, reapplied as you go, prevents the soreness that repeated watery stools cause.
Stay near a toilet
Movements usually start within one to two hours of the first dose and come in waves. Keep the evening free and stay home.
Slow down before stopping
Nausea is the most common reason people give up. A break of twenty to thirty minutes and then continuing is often all it takes.
Stop and call the clinic if you are vomiting and cannot keep the solution down, if you have severe abdominal pain, or if you feel faint and unable to drink. There is more than one preparation, and the appointment can move. Neither of those is a failure on your part.
Common questions
Questions people ask about the prep.
The five that come up most often in clinic, answered the way his team answers them on the phone.
What happens if I cannot finish the bowel prep solution?
Tell the clinic rather than simply stopping, because the answer depends on how far through you are and what your stools look like. If you have finished most of the solution and your stools are already running clear, the preparation may well be adequate. If you stopped early and your stools are still brown or solid, the examination is unlikely to be reliable, and we would usually rather adjust the plan than proceed. Nausea is the most common reason people stop, and slowing down, taking a break of twenty to thirty minutes and then continuing is often enough.
Is it normal to feel unwell while taking the preparation?
Some nausea, bloating and cramping is common and expected, particularly with the first dose. Chilling the solution, sipping it slowly and having a clear chaser to hand all help. If you are vomiting and cannot keep the solution down, have severe abdominal pain, or feel faint and unable to drink, stop and call the clinic. We can advise whether to continue, switch to a different preparation, or move the appointment.
How long before the colonoscopy do I need to stop eating and drinking?
You will usually be asked to stop solid food from the start of the clear liquid day, and to stop all liquids, including water, some hours before your appointment. That final cutoff is set by the anaesthetic requirement rather than by the bowel preparation, so follow the hours the clinic gives you rather than a number from a website.
Why is the dose split into two?
Because the evidence is that splitting it cleans the colon better than taking the whole preparation the night before. The joint recommendation of the American College of Gastroenterology, the American Gastroenterological Association and the American Society for Gastrointestinal Endoscopy (source: US Multi-Society Task Force on Colorectal Cancer, bowel preparation consensus recommendations (ACG, AGA and ASGE), opens in a new tab) is to use a split-dose regimen, and two separate meta-analyses of controlled trials (source: Bucci C, et al. Optimal bowel cleansing for colonoscopy: split the dose. Gastrointestinal Endoscopy, 2014, opens in a new tab) reached the same conclusion. It is more inconvenient and it is the reason the view is clearer.
What if my preparation was not good enough on the day?
If the view is poor, the reliable answer is to repeat the examination rather than to report a scope that could not see properly. That is disruptive, and it is the reason the preparation is worth the effort the first time. If the clinic thinks the preparation is falling short while you are still at home, we would rather hear from you that evening than discover it in the endoscopy suite.
Ask about your preparation
Not sure the prep is going to plan?
His team goes through the preparation with you before the day, including any adjustment your medicines or medical history call for.