High-quality bowel preparation is a crucial pre-requisite for successful colonoscopy. Inadequate bowel preparation is associated with lower polyp and adenoma detection rates, longer procedure time, increased need for repeat procedures, higher cost and a higher rate of patient drop out from screening programs.
With these considerations, overseas guidelines have recommended acceptable rates of bowel preparation adequacy, ranging from 85% (American Society for Gastrointestinal Endoscopy) to 90% (European Society for Gastroenterology).
The ideal bowel preparation should be safe, effective and well tolerated but a single preparation type and dosing regimen will not suit all patients. Safe bowel preparation requires an understanding of preparation types and their potential adverse outcomes. Preparation timing is important for efficacy and dietary preparation has implications for satisfaction and tolerance. Understanding the risk factors for poor preparation helps individualise regimens for optimal outcome.
Overview of evidence (non-systematic literature review)
No systematic reviews were undertaken for this topic. Practice points were based on selected evidence and guidelines (see Guideline development process).
Available bowel preparation types
Most bowel preparations are based on an osmotic mechanism of action and work by retaining or drawing fluid into the bowel lumen (Table 1). Some also contain a stimulant. Polyethylene glycol (PEG)-based preparations generally have a good safety profile and should be considered the first choice for patients of older age or with organ dysfunction including renal failure, heart failure or cirrhosis.
Combination preparations with sodium picosulfate, magnesium oxide and citric acid both contain osmotic and stimulant effects. They are lower in volume than PEG-based preparations, which may enhance compliance but may also increase the risk of dehydration if adequate additional fluids are not consumed. They should be used with caution in the elderly, those with renal impairment and those at risk of dehydration.
Sodium phosphate is a potent hyperosmotic preparation. It has been associated with cases of acute kidney injury and phosphate nephropathy causing irreversible renal failure. This preparation should be avoided in those of older age, those with kidney, heart or liver disease, inflammatory bowel disease (IBD), and those on medications that alter renal blood flow/electrolytes.
There is limited evidence from head to head efficacy studies on which to recommend one specific type of bowel preparation over another. However, lower volume PEG-based preparations appear to be as effective as high volume PEG-based preparations.Table 1. Main types of bowel preparation currently used in Australia
|Main ingredient||Action||Main types||Volume
(without clear fluids)
PEG + ascorbate components
PEG + ascorbate components
|1000mL x 3
1000mL x 2*#500mL x 2*#
Safe and effective
Modest fluid/electrolyte shift when consumed as per recommendations
First choice for patients with: renal failure, heart failure, cirrhosis, IBD, older age
|Larger volumes may be less well tolerated|
|Sodium picosulfate, magnesium oxide, citric acid||Stimulant and osmotic||Sodium picosulfate + magnesium oxide and citric acid||250mL x 2*‡||Lower volume||Generally well tolerated
Beware in renal impairment (transient hyper-magnesemia)
Beware dehydration (consider PEG-based preparation in elderly/comorbidities)
|Sodium phosphate||Hyperosmotic||Sodium phosphate liquid§ Sodium phosphate tablets§||45mL x 2
|Low volume or tablet form||Risk of dehydration and acute kidney injury
Risk of phosphate nephropathy and irreversible renal failure
| Abbreviations: PEG: Polyethylene glycol; IBD: inflammatory bowel disease; *recommended additional minimum of 500mL clear fluids per dose; §750mL minimum additional clear fluid recommended per dose; #recommend avoiding in G6PG deficiency; ‡recommend avoiding in phenylketonuria.
Note: This table does not list all commercially available bowel preparations. Some companies create combination kits containing more than one form of bowel preparation.
The timing of bowel preparation is one of the most important factors associated with optimal bowel preparation. Split-dose bowel preparation is associated with a significantly increased chance of successful bowel preparation when compared with traditional ‘day-prior’ preparation. In a meta-analysis, success with spit-dose preparation compared with day-prior preparation was 85% versus 63% (absolute difference 22%; confidence intervalA measure that quantifies the uncertainty in measurement. When reported as 95% CI, it is the range of values within which we can be 95% sure that the true value for the whole population lies. [CI] 16–27%).
The runway time or timing of the last dose prior to the procedure is also important. In the meta-analysis by Bucci et al, there was a significantly greater chance of preparation success when the last dose was taken ≤3 hours or 4–5 hours prior to the colonoscopy as compared with >5 hours prior to the colonoscopy. Taking bowel preparation within 3–5 hours of the procedure is also likely to be safe from an anaesthetic viewpoint. A meta-analysis of six separate randomised control trials found no significant difference in the gastric residual volume of patients having a split-dosed procedure as compared to a day-prior preparation or no preparation.
‘Same-day’ bowel preparation is when the entire preparation is taken on the same day as the colonoscopy. In a meta-analysis, same-day preparation had a similar efficacy and patient tolerance to a split-dose preparation.Back to top
Several low residue diets are as effective as a clear fluid restriction prior to colonoscopy with significantly increased patient satisfaction and tolerability. Low residue diets such as the 'white diet' (Table 2) can be used on the day(s) prior to colonoscopy in a split-dose preparation regimen without impairing the quality of the preparation, while achieving significant improvements in patient satisfaction and tolerability. This is also likely to be effective with same-day preparation.
Table 2. Food and fluids permitted in the white diet and those not allowed
|Foods & fluids permitted||Milk (regular, low fat, skim), water, lemonade, soda or mineral water, clear (not coloured) sports drinks
White-coloured yoghurt (no added fruit or insulin), mayonnaise, cream, sour cream, butter and margarine, oil for cooking
Regular white bread/toast, popped rice cereal (e.g. Rice Bubbles), eggs
White rice, regular pasta, potatoes (peeled), rice noodles
Plain rice crackers, white flour, sugar
Chicken breast (no skin), white fish fillet (no skin)
Plain cream cheese, cheddar cheese, ricotta, fetta, cottage, parmesan or mozzarella cheese, white sauce, white chocolate, vanilla ice cream, lemonade ice-block (e.g. ‘Icy-pole’), clear jelly, custard, 'milk bottles' (white confectionery)
|Foods not allowed||Anything not listed above
Other white-coloured foods such as pears, parsnip, cauliflower, onion, high fibre white bread, tofu, coconut, porridge, banana, mushrooms, semolina, couscous, popcorn
|Source: Butt et al (2016).|
Factors associated with poor preparation
Factors associated with an increased risk of poor bowel preparation include reduced health literacy, older age, constipation, chronic diseases, diabetes, cirrhosis, neurological conditions such as stroke and dementia, immobility, spinal injury, prior gastrointestinal surgery, opioids and antidepressant medication.
Providing larger volumes of bowel preparation in a split dose should be considered for patients at significant risk of poor preparation or those with a history of inadequate bowel preparation. In a study of patients with a prior poor bowel preparation, success rate was higher among those randomised to 4L split-dosed PEG than those randomised to 2L split-dosed PEG: 81.1% versus 67.4% odds ratioA comparison of the odds (probability) of something happening in one group with the odds of it happening in another. [OR] 2.07; CI: 1.163–3.689). Validated scoring systems such as the one by Gimeno-Garcia et al may help in identifying those at risk of poor preparation, but a corresponding management algorithm is awaited.
Documentation of bowel preparation
The quality of bowel preparation should be documented on every colonoscopy report using a validated score, ideally after cleaning has been performed. The Boston Bowel Preparation Scale (BPPS) is the most validated score and is recommended. The Ottawa scale requires documentation of stool volume so may be less clinically applicable, and Harefield cleansing scale is detailed and thus probably better suited to research. The Aronchick scale is an insertion scale with simple categories, which is often used in electronic endoscopy reporting systems. The following scores indicate successful bowel preparation:
|Harefield cleansing scale||Total score A or B|
|Aronchick scale||Excellent, good, or fair|
High-quality bowel preparation is a crucial pre-requisite for successful colonoscopy. Optimal preparation is achieved with split-dose or same-day preparation timing.
PEG-based bowel preparations are safer for those with co-morbidities and the elderly.
A low-residue diet can be used on the days prior to colonoscopy with appropriate preparation timing.
Factors associated with poor preparation should be assessed and patients at high risk of poor preparation should be offered additional preparation volume and split-dose timing.
Preparation quality should be documented on the colonoscopy report using a validated preparation scale.
Where the preparation is inadequate, repeat colonoscopy should normally be offered within 12 months.
Successful bowel preparation should be achieved in ≥90% of all colonoscopies.
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