Bowel preparation

From Clinical Guidelines Wiki


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.[1][2][3][4][5][6]

With these considerations, overseas guidelines have recommended acceptable rates of bowel preparation adequacy, ranging from 85% (American Society for Gastrointestinal Endoscopy[7]) to 90% (European Society for Gastroenterology[8]).

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.

Back to top

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.[9][10]

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.[11][12]Table 1. Main types of bowel preparation currently used in Australia

Main ingredient Action Main types Volume

(without clear fluids)

Pro Con
PEG Osmotic PEG

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

32 tablets

Low volume or tablet form Risk of dehydration and acute kidney injury

Risk of phosphate nephropathy and irreversible renal failure

Avoid in:

  • elderly
  • heart failure
  • renal impairment
  • cirrhosis
  • IBD
  • patients on medications that alter renal blood flow/electrolytes
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.

Back to top

Preparation timing

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%).[13]

The runway time or timing of the last dose prior to the procedure is also important.[13][14] 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.[13] 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.[15]

‘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.[16]Back to top

Dietary preparation

Several low residue diets are as effective as a clear fluid restriction prior to colonoscopy with significantly increased patient satisfaction and tolerability.[17][18][19] 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.[17] 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.[20][21][22]

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).[23] Validated scoring systems such as the one by Gimeno-Garcia et al[22] may help in identifying those at risk of poor preparation, but a corresponding management algorithm is awaited.

Back to top

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.[24] The Ottawa scale[25] requires documentation of stool volume so may be less clinically applicable, and Harefield cleansing scale is detailed and thus probably better suited to research.[26] The Aronchick scale[27] is an insertion scale with simple categories, which is often used in electronic endoscopy reporting systems. The following scores indicate successful bowel preparation:

Ottawa scale ≤7
Harefield cleansing scale Total score A or B
Aronchick scale Excellent, good, or fair

Whichever scale is used, inadequate preparation should be clearly documented and those with inadequate preparation should be offered repeat colonoscopy within 12 months.[7]Back to top

Practice pointQuestion mark transparent.png

High-quality bowel preparation is a crucial pre-requisite for successful colonoscopy. Optimal preparation is achieved with split-dose or same-day preparation timing.

Practice pointQuestion mark transparent.png

PEG-based bowel preparations are safer for those with co-morbidities and the elderly.

Practice pointQuestion mark transparent.png

A low-residue diet can be used on the days prior to colonoscopy with appropriate preparation timing.

Practice pointQuestion mark transparent.png

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.

Practice pointQuestion mark transparent.png

Preparation quality should be documented on the colonoscopy report using a validated preparation scale.

Practice pointQuestion mark transparent.png

Where the preparation is inadequate, repeat colonoscopy should normally be offered within 12 months.

Practice pointQuestion mark transparent.png

Successful bowel preparation should be achieved in ≥90% of all colonoscopies.

Back to top


  1. Froehlich F, Wietlisbach V, Gonvers JJ, Burnand B, Vader JP. Impact of colonic cleansing on quality and diagnostic yield of colonoscopy: the European Panel of Appropriateness of Gastrointestinal Endoscopy European multicenter study. Gastrointest Endosc 2005 Mar;61(3):378-84 Abstract available at
  2. Harewood GC, Sharma VK, de Garmo P. Impact of colonoscopy preparation quality on detection of suspected colonic neoplasia. Gastrointest Endosc 2003 Jul;58(1):76-9 Abstract available at
  3. Parra-Blanco A, Nicolas-Perez D, Gimeno-Garcia A, Grosso B, Jimenez A, Ortega J, et al. The timing of bowel preparation before colonoscopy determines the quality of cleansing, and is a significant factor contributing to the detection of flat lesions: a randomized study. World J Gastroenterol 2006 Oct 14;12(38):6161-6 Abstract available at
  4. Rex DK, Imperiale TF, Latinovich DR, Bratcher LL. Impact of bowel preparation on efficiency and cost of colonoscopy. Am J Gastroenterol 2002 Jul;97(7):1696-700 Abstract available at
  5. Cohen LB. Advances in bowel preparation for colonoscopy. Gastrointest Endosc Clin N Am 2015 Apr;25(2):183-97 Abstract available at
  6. Sulz MC, Kröger A, Prakash M, Manser CN, Heinrich H, Misselwitz B. Meta-Analysis of the Effect of Bowel Preparation on Adenoma Detection: Early Adenomas Affected Stronger than Advanced Adenomas. PLoS One 2016;11(6):e0154149 Abstract available at
  7. 7.07.1 Saltzman JR, Cash BD, Pasha SF, Early DS, Muthusamy VR, Khashab MA, et al. Bowel preparation before colonoscopy. Gastrointest Endosc 2015 Apr;81(4):781-94 Abstract available at
  8. Kaminski MF, Thomas-Gibson S, Bugajski M, Bretthauer M, Rees CJ, Dekker E, et al. Performance measures for lower gastrointestinal endoscopy: a European Society of Gastrointestinal Endoscopy (ESGE) quality improvement initiative. United European Gastroenterol J 2017 Apr;5(3):309-334 Abstract available at
  9. Heher EC, Thier SO, Rennke H, Humphreys BD. Adverse renal and metabolic effects associated with oral sodium phosphate bowel preparation. Clin J Am Soc Nephrol 2008 Sep;3(5):1494-503 Abstract available at
  10. Bechtold ML, Mir F, Puli SR, Nguyen DL. Optimizing bowel preparation for colonoscopy: a guide to enhance quality of visualization. Ann Gastroenterol 2016 Apr;29(2):137-46 Abstract available at
  11. Jung YS, Lee CK, Eun CS, Park DI, Han DS, Kim HJ. Low-Volume Polyethylene Glycol with Ascorbic Acid for Colonoscopy Preparation in Elderly Patients: A Randomized Multicenter Study. Digestion 2016;94(2):82-91 Abstract available at
  12. Clark RE, Godfrey JD, Choudhary A, Ashraf I, Matteson ML, Bechtold ML. Low-volume polyethylene glycol and bisacodyl for bowel preparation prior to colonoscopy: a meta-analysis. Ann Gastroenterol 2013;26(4):319-324 Abstract available at
  13. Bucci C, Rotondano G, Hassan C, Rea M, Bianco MA, Cipolletta L, et al. Optimal bowel cleansing for colonoscopy: split the dose! A series of meta-analyses of controlled studies. Gastrointest Endosc 2014 Oct;80(4):566-576.e2 Abstract available at
  14. Siddiqui AA, Yang K, Spechler SJ, Cryer B, Davila R, Cipher D, et al. Duration of the interval between the completion of bowel preparation and the start of colonoscopy predicts bowel-preparation quality. Gastrointest Endosc 2009 Mar;69(3 Pt 2):700-6 Abstract available at
  15. Avalos DJ, Michael M, Castro-Pavia F, Sussman D, Gonzalez Martinez JL, Dwivedi A et al. Sa1061 Split-Dose Bowel Preparation Does Not Increase Gastric Residual Volume as Compared With Day Prior Preparations: A Systematic Review and Network Meta-Analysis. GIE 2017 May;Volume 85, Issue 5, Supplement: AB174-AB175. Abstract available at
  16. Avalos DJ, Castro FJ, Zuckerman MJ, Keihanian T, Berry AC, Nutter B, et al. Bowel Preparations Administered the Morning of Colonoscopy Provide Similar Efficacy to a Split Dose Regimen: A Meta Analysis. J Clin Gastroenterol 2017 Sep 6 Abstract available at
  17. 17.017.1 Butt J, Bunn C, Paul E, Gibson P, Brown G. The White Diet is preferred, better tolerated, and non-inferior to a clear-fluid diet for bowel preparation: A randomized controlled trial. J Gastroenterol Hepatol 2016 Feb;31(2):355-63 Abstract available at
  18. Nguyen DL, Jamal MM, Nguyen ET, Puli SR, Bechtold ML. Low-residue versus clear liquid diet before colonoscopy: a meta-analysis of randomized, controlled trials. Gastrointest Endosc 2016 Mar;83(3):499-507.e1 Abstract available at
  19. Avalos DJ, Sussman DA, Lara LF, Sarkis FS, Castro FJ. Effect of Diet Liberalization on Bowel Preparation. South Med J 2017 Jun;110(6):399-407 Abstract available at
  20. Gandhi K, Tofani C, Sokach C, Patel D, Kastenberg D, Daskalakis C. Patient Characteristics Associated With Quality of Colonoscopy Preparation: A Systematic Review and Meta-Analysis. Clin Gastroenterol Hepatol 2017 Aug 18 Abstract available at
  21. Govani SM, Elliott EE, Menees SB, Judd SL, Saini SD, Anastassiades CP, et al. Predictors of suboptimal bowel preparation in asymptomatic patients undergoing average-risk screening colonoscopy. World J Gastrointest Endosc 2016 Sep 16;8(17):616-22 Abstract available at
  22. 22.022.1 Gimeno-García AZ, Baute JL, Hernandez G, Morales D, Gonzalez-Pérez CD, Nicolás-Pérez D, et al. Risk factors for inadequate bowel preparation: a validated predictive score. Endoscopy 2017 Jun;49(6):536-543 Abstract available at
  23. Gimeno-García AZ, Hernandez G, Aldea A, Nicolás-Pérez D, Jiménez A, Carrillo M, et al. Comparison of Two Intensive Bowel Cleansing Regimens in Patients With Previous Poor Bowel Preparation: A Randomized Controlled Study. Am J Gastroenterol 2017 Jun;112(6):951-958 Abstract available at
  24. Calderwood AH, Jacobson BC. Comprehensive validation of the Boston Bowel Preparation Scale. Gastrointest Endosc 2010 Oct;72(4):686-92 Abstract available at
  25. Rostom A, Jolicoeur E. Validation of a new scale for the assessment of bowel preparation quality. Gastrointest Endosc 2004 Apr;59(4):482-6 Abstract available at
  26. Halphen M, Heresbach D, Gruss HJ, Belsey J. Validation of the Harefield Cleansing Scale: a tool for the evaluation of bowel cleansing quality in both research and clinical practice. Gastrointest Endosc 2013 Jul;78(1):121-31 Abstract available at
  27. Aronchick CA, Lipshutz WH, Wright SH, Dufrayne F, Bergman G. A novel tableted purgative for colonoscopic preparation: efficacy and safety comparisons with Colyte and Fleet Phospho-Soda. Gastrointest Endosc 2000 Sep;52(3):346-52 Abstract available at

Back to top