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Abstract

Colorectal cancer remains a major global health concern, highlighting the critical importance of effective colonoscopy, whose success depends on high-quality bowel preparation. Inadequate preparation is common and leads to prolonged procedure, and missed polyps and adenomas. It is important to recognize that not all individuals can attain adequate bowel preparation through a uniform regimen. Various risk factors influencing bowel preparation quality have been reported, and different laxative regimens each present distinct advantages and limitations. Understanding these elements can help improve patient bowel preparation outcomes. This is a narrative review. This article attempts to summarize available clinical trials and evidence regarding strategies to optimize bowel preparation for individuals.

Keywords

Bowel preparation colonoscopy individuals risk factors laxatives

Introduction

Colorectal cancer (CRC) stands as the second most prevalent cause of death attributed to cancer in the United States.¹ Colonoscopy plays a pivotal role in the screening process for CRC.^2–4 However, the efficacy of this procedure heavily relies on the quality of bowel preparation. Adequate bowel cleanliness significantly improves the polyp detection rate (PDR) and adenoma detection rate (ADR).⁵ Conversely, inadequate bowel preparation may lead to bad visualization, resulting in diminished ADR and PDR.⁶ Moreover, poor bowel cleanliness may even cause incomplete procedures, potentially necessitating early repeat colonoscopy (within a year).^7–9

Several studies have indicated that specific patients are predisposed to experiencing inadequate bowel preparation due to specific factors such as comorbidities, medication use.^10,11 Consequently, a uniform laxative regimen may not effectively meet the needs of every patient. There are several commercially available bowel preparation agents, each with distinct mechanisms and limitations.¹² Therefore, it is critical to tailor the selection of laxative regimens to individual requirements. Supplying patients with individualized laxative strategies can not only elevate the overall quality of bowel preparation but also improve patient tolerance and adherence.^13,14 In addition, there is growing emphasis on addressing issues such as how to predict and manage patients at high risk for inadequate bowel preparation, as well as rescue strategies following preparation failure. While earlier studies have identified risk factors for inadequate preparation, and others have compared the efficacy of various laxatives, our article synthesizes these disparate strands of evidence into a practical framework for individualized bowel preparation, emphasizing the critical role of tailored bowel preparation in optimizing colonoscopy outcomes. This narrative review retrieves and organizes recent literature concerning bowel preparation from databases including PubMed, Web of Science, Embase, and Scopus.

Methods

A comprehensive search of the English language literature was conducted across four databases, including PubMed, Web of Science, Embase, and Scopus databases, covering publications up to 31 October 2025. This search strategy combined all possible key terms “colonoscopy,” “bowel preparation,” “bowel cleansing,” “laxatives,” and “colorectal cancer” along with medical Subject headings (MeSH) terms.

The importance of bowel preparation

Epidemiology of CRC

CRC represents a major global health burden. According to GLOBOCAN 2020, CRC ranked as the third most commonly diagnosed cancer and the second leading cause of cancer-related mortality worldwide.¹⁵ Recent data from the United States (2023)¹⁶ and China (2022)¹⁷ consistently place CRC among the top malignancies in both incidence and mortality. Beyond its clinical impact, CRC significantly impairs patients’ quality of life and imposes a substantial economic burden. Hence, there is an urgent need to heighten public awareness and prioritize early detection and intervention.

Significance of colonoscopy

CRC in its early stages is frequently asymptomatic, leading to low patient awareness and delayed diagnosis. When symptoms like hematochezia, abdominal pain, or weight loss appear, the disease is often diagnosed at an advanced stage, typically requiring invasive treatments such as surgery or chemoradiotherapy. The 5-year relative survival rate for CRC drops markedly from approximately 90% in localized disease to only about 14% in metastasis cases.¹⁸

Despite the poor prognosis of advanced CRC, it takes approximately 5 to 10 years for precancerous lesions to evolve into CRC, presenting a critical window for early detection and intervention. A variety of screening methods exist for CRC, including stool-based screening tests, colonoscopy, computed tomographic (CT) colonography, capsule endoscopy, and blood-based screening tests. Among these, colonoscopy plays a central role, as it enables direct visualization and removal of precancerous polyps, particularly advanced adenomas.² The U.S. Preventive Services Task Force (USPSTF) strongly supports CRC screening for adults aged 50 to 75 years, emphasizing its substantial overall health benefits.¹⁹ Studies have verified that CRC screening through sigmoidoscopy or colonoscopy can significantly diminish the incidence and mortality of CRC.^3,4 Most CRCs develop from polyps.²⁰ Colonoscopy with polypectomy is effective in lowering population-level risk of CRC. Moreover, early-stage CRC (such as T1 tumors) can be managed through colonoscopy via techniques including endoscopic mucosal resection and endoscopic submucosal dissection, depending on lesion size and morphology.²⁰

Importance of bowel preparation

Colonoscopy represents an essential instrument for the screening and diagnosis of bowel lesions. Nevertheless, its efficacy is profoundly influenced by the quality of bowel preparation before the procedure. Bowel preparation involves dietary modifications and the administration of cleansing agents, usually oral laxatives or enemas, aimed at cleansing the colon and attaining optimal mucosal visualization during colonoscopy. An adequate bowel preparation rate of ≥90%, as defined by American Society for Gastrointestinal Endoscopy/American College of Gastroenterology (ASGE/ACG) guidelines, is a key quality indicator for colonoscopy.²¹ High-quality bowel preparation is essential for colonoscopy. It provides clear visibility of the intestinal mucosa, reducing the chance of missing lesions or early tumors.⁵ Besides, adequate preparation significantly boosts the efficiency of colonoscopy. Inadequate bowel preparation, conversely, is correlated with lower PDR and ADR.^22,23 Furthermore, poor bowel cleanliness may even prevent completion of the colonoscopy. A study of 9962 procedures revealed that 11% of colonoscopies were incomplete, with inadequate bowel preparation accounting for 82% of these cases.⁷ For these reasons, multiple guidelines recommend early repeat colonoscopy (within a year) for individuals with poor preparation quality.^8,9

Factors affecting the quality of bowel preparation

Inadequate bowel preparation remains a common challenge in colonoscopy, affecting up to one in four procedures.²⁴ Multiple patient-related factors contribute to this issue, including advanced age, male gender, obesity, hospitalization, history of constipation, diabetes, hypertension, cirrhosis, prior stroke, use of anesthesia, and intake of tricyclic antidepressants.^10,11,25 A recent meta-analysis identified health conditions and specific medication use as more significant predictors of inadequate bowel preparation than sociodemographic factors.²⁶ However, poor adherence, often driven by misconceptions and insufficient awareness also substantially compromises preparation quality. A European survey on colonoscopy revealed significant public misunderstandings regarding its purpose, the subjective experience during the procedure, and the required volume of bowel preparation.²⁷ Common patient misconceptions include: (1) underestimating the importance of rigorous preparation; (2) believing that fasting alone is sufficient; (3) assuming that a few bowel movements indicate completion of cleansing; and (4) thinking that increased water intake directly improves colonoscopy effectiveness. Other factors affecting compliance and bowel cleanliness include dietary restrictions, the high-volume fluid intake, and the unpleasant taste of laxatives. Additionally, individuals with lower education levels may struggle to fully understand preparation instructions, ultimately leading to poorer adherence and suboptimal results.^28,29 To help address these challenges, several predictive scoring models have been developed to identify patients at high risk of inadequate preparation.^30,31 Using these tools, clinicians can identify patients at high risk and provide more individualized guidance and support to optimize bowel cleansing. Table 1 summarizes the key predictors of inadequate bowel preparation based on recent meta-analyses.

Table 1.

Summary of predictive factors for inadequate bowel preparation.

	Classification	Predictive factors	Adjusted odds ratio
Azizullah et al.³²	Sociodemographic	Age ≥ 65 years	1.30 (1.07–1.57)
		BMI ≥ 25	1.27 (1.13–1.44)
		Low education level	1.26 (1.08–1.46)
	Comorbidity-related	Psychiatric disease	2.46 (1.47–4.14)
		Liver cirrhosis	2.43 (1.58–3.73)
		Constipation	1.95 (1.71–2.21)
		Diabetes mellitus	1.79 (1.62–1.98)
		Previous abdominopelvic surgery	1.71 (1.33–2.20)
		Hematochezia	1.57 (1.33–2.20)
	Medication-related	Tricyclic antidepressant use	2.41 (1.48–3.92)
	Procedure-related	Incomplete bowel preparation intake	3.27 (2.62–4.08)
		Lack of split-dose bowel preparation	2.67 (2.17–3.29)
		Nonadherence to dietary instructions	2.47 (1.94–3.14)
Zhang et al.³³	Comorbidity-related	History of abdominal surgery	2.72 (2.07–3.56)
		Constipation	3.56 (2.41–5.25)
		Diabetes mellitus	2.54 (1.81–3.57)
	Procedure-related	Noncompliance with the diet regimen	2.51 (1.96–3.21)
		Incomplete intake of laxative	2.43 (1.60–3.67)
		Inadequate exercise during preparation	3.13 (2.39–4.11)
Feng et al.³⁴	Comorbidity-related	Constipation	1.74 (1.43–2.10)
		Diabetes mellitus	1.87 (1.61–2.16)
		Previous abdominal/pelvic surgery	1.76 (1.38–2.25)
		Parkinson's disease	2.42 (1.32–4.43)
		Previous inadequate bowel preparation	1.98 (1.31–3.00)
	Medication-related	Tricyclic antidepressants	2.00 (1.29–3.10)
	Procedure-related	Characteristics of last stool	4.32 (2.81–6.65)
	Procedure-related	Incomplete preparation intake	2.82 (2.09–3.81)

BMI: body mass index.

Bowel preparation quality scales

To standardize the evaluation of bowel cleanliness, several validated assessment scales have been developed worldwide. Among them, the Boston Bowel Preparation Scale (BBPS) and the Ottawa Bowel Preparation Scale (OBPS) are the most widely recognized and applied.

The BBPS divides the colon into three segments: right, transverse, and left. Each segment is scored from 0 to 3 based on mucosal visibility following flushing and suction. This scale does not assess fluid volume. A total BBPS score ≥6, with each segment scoring ≥2, generally indicates adequate preparation.⁶ A study involving 438 men showed that patients with a BBPS score of 2 or 3 in each colonic segment had adequate bowel preparation for detecting adenomas larger than 5 mm.³⁵ Furthermore, the BBPS score was also associated with the recommended interval for repeat colonoscopy.³⁶

In contrast, the OBPS both assesses cleanliness and fluid volume.³⁷ It assigns a cleanliness score (0–4) to each of three colon segments (right, mid, and rectosigmoid). Combined with a global fluid quantity score (0–2), it yields a total ranging from 0 to 14, where a lower total indicates better preparation. Unlike the BBPS, the OBPS lacks a universally accepted cutoff for adequate preparation, though a score ≥8 often predicts inadequate cleansing.³⁸ Studies have found no significant difference between the OBPS and the BBPS in measuring PDR or ADR.³⁹ Nevertheless, a major systematic review comparing various bowel preparation scales established the BBPS as the most reliable and thoroughly validated instrument.⁴⁰

Individualized management of bowel preparation

Definition of individualized management

Individualized management follows the principle of administering the precise medication, in the exact dosage, to the right patient, at the right time, and via the most suitable route.⁴¹ Given the inherent variability among patients, the effectiveness and adverse reactions of bowel preparation regimens vary significantly. Likewise, responses to different laxatives may differ from person to person. Through individualized regimens, patients can avoid unnecessary interventions and achieve optimal outcomes with minimal discomfort in the shortest time possible. Tailored bowel-cleansing regimens may improve preparation quality without increasing the risk of adverse effects, thereby enhancing colonoscopy efficiency and patient satisfaction.

Why consider individualized bowel preparation management?

Patients may experience inadequate bowel preparation due to a multitude of factors, such as their underlying disease or the specific medications they are taking. The diversity of available bowel preparation methods provides a solid basis for customizing bowel preparation strategies.¹² Standard laxative protocols often prove insufficient for specific patient subgroups. The appropriate population and contraindications differ for each laxatives class; therefore, the selection for an individual patient should take these factors into consideration. For example, diabetic patients tend to have poorer preparation quality than nondiabetics on the same polyethylene glycol (PEG) regimen, highlighting the limitation of standardized protocols in this population.⁴² Similarly, patients with prior colon resection (particularly with an intact right colon) frequently have suboptimal preparation compared to those without surgery.⁴² Oral sodium phosphate (OSP) solutions may appear more effective than PEG in patients with constipation, but the level of evidence was relatively lower.⁴³ Evidence supports personalized strategies to improve bowel preparation quality.^13,14 Low-volume bowel preparation regimens may be considered, as they offer adequate cleansing with improved tolerability.^44–46 However, more data are needed for high-risk groups. Accounting for individual characteristics helps optimize preparation and may ultimately improve colonoscopy outcomes.

Specific measures of individualized management

Prebowel preparation

Patient education for bowel preparation

The timing of bowel preparation initiation should be carefully aligned with the scheduled colonoscopy appointment. Adequate patient education before colonoscopy involves explaining the importance of preparation and the steps by providing clear instructions. The reinforced approach may improve bowel preparation quality, increase ADR and PDR, and decrease insertion and withdrawal time and adverse events.⁴⁷ In practice, effective patient education relies on the following evidence-based tools,^14,48–51 including: (1) structured oral and written explanation: individualized instructions from a clinician, supported by materials such as illustrated booklets, cartoons, or pictorial guides; (2) Digital Reminders: timely telephone calls or short message services to reinforce preparation timing, fluid intake, and medication adherence; (3) Visual aids: simplified educational videos using plain language and animations to demonstrate key steps and common errors; (4) Smartphone applications: mobile applications (e.g. WeChat-based tools or dedicated healthcare applications) that offer colonoscopy education, medication reminders, and self-assessment of stool quality; (5) Educational virtual reality (VR): immersive VR videos that simulate the preparation process and colonoscopy procedure, helping to reduce anxiety and improve patient understanding.

Informed by patient education, individuals should adopt a low-residue diet in the days preceding colonoscopy. Supported by current evidence and the latest consensus of US Multi-Society Task Force on Colorectal Cancer, this approach is favored over traditional clear liquid diets. It demonstrates superior tolerability, higher acceptance, and greater willingness to repeat, while maintaining noninferior cleansing quality and safety.^36,52,53 For most patients, a single-day low-residue diet is sufficient to achieve adequate bowel preparation.^54,55 However, for those at high risk of inadequate preparation, extending the duration of low-residue diet may be necessary to ensure optimal cleansing.

Laxatives

Effective bowel preparation is essential for high-quality colonoscopy, requiring a laxative strategy considering the sociodemographic factors, medical history, medications, and prior bowel preparation quality.⁵⁶ This section outlines evidence-based laxatives recommendations for general and specific patient populations.

General patients

For healthy individuals, various laxative regimens achieve adequate bowel cleansing (≥90%), with common options summarized in Table 2.

Table 2.

Summary of common bowel preparation laxatives.

Laxatives	Dosing timing	Volume	Efficacy	Limitations	Contraindications
High volume PEG	Split-dose; Single dose (same day)	4L	Noninferior or superior to non-PEG regimens and 2L PEG plus ascorbate	High volume and least tolerable	Congestive cardiac failure (NYHA class III or IV)
Low-volume PEG + ascorbate	Split-dose; Single dose (same day)	2L	Noninferior or superior to all other laxatives	Caution in patients with glucose-6-phosphate dehydrogenase deficiency and severe renal insufficiency	Congestive heart failure (NYHA III or IV)
OSS	Split dose	2 bottles (177mL, dilute to 0.5L) plus 2L H₂O	Noninferior to high and low volume PEG	Risk of mucosal inflammation, ulceration, and morphological changes	Congestive heart failure; Active IBD; Ascites; Severe renal insufficiency (creatinine clearance < 30mL/min)
OSP	Split dose	1 bottle (90mL, dilute to 1.5L)	Noninferior to high and low volume PEG	Risk of acute phosphate nephropathy and associated renal impairment	Congestive heart failure; Ascites; Severe renal insufficiency (creatinine clearance < 30mL/min)
SPMC	Split dose	2 packets (dissolve to 150mL) plus 2.3L H₂O	Noninferior to high and low volume PEG; Better tolerated in children	Risk of intestinal inflammation; High cost	Congestive heart failure; Severe renal insufficiency (creatinine clearance < 30mL/min); Active IBD; Hypermagnesemia; Rhabdomyolysis

IBD, inflammatory bowel disease; OSS, oral sulfate solution; OSP, oral sodium phosphate; PEG, polyethylene glycol; SPMC, sodium picosulfate/magnesium citrate.

PEG-based regimens are most commonly used, though preferred volumes vary geographically. Western guidelines often recommend 4L PEG, whereas Chinese guidelines favor 3L PEG, reflecting differences in patient tolerance and body habitus.^57,58 Compared to monotherapy, low-volume regimens combined with adjuvants may enhance cleansing efficacy.^59–61 Recent meta-analyses indicate that low-volume 2L PEG with adjuvants (e.g. simethicone, lactulose, and bisacodyl) provides efficacy comparable to 4L PEG, alongside better tolerance and willingness to repeat.^44,62 A network meta-analysis of 22 randomized controlled trials (RCTs) further supports that 2L PEG combined with simethicone or lactulose may outperform 2L PEG plus ascorbate or 4L PEG with simethicone.⁶³ Besides, for low-risk populations with inadequate bowel preparation, a single-dose regimen of 2L PEG may be considered a viable alternative. Together, these findings provides updated evidence supporting individualized bowel preparation strategies.

Specific patient groups

For specific patients, laxatives must ensure both safety and tolerability as well as effectiveness.

Older adults often experience inadequate preparation due to comorbidities and polypharmacy. Low-volume regimens (e.g. 2L PEG with ascorbic acid or oral sulfate solution) are better tolerated and equally effective compared to high-volume PEG.^64–67 Therefore, a split-dose, low-volume regimen, with adjuvants as needed, may be considered to improve bowel preparation quality in this group.

Pregnant women requiring endoscopy should use PEG-based regimens.⁶⁸

Children may be prescribed PEG, sodium picosulfate/magnesium citrate (SPMC), or senna. Multiple meta-analyses and clinical studies indicate that both PEG and SPMC are effective and safe; however, SPMC is often preferred due to better acceptability.^69–71

Patients with acute lower gastrointestinal bleeding should receive PEG before emergency colonoscopy.⁷²

Inflammatory bowel disease (IBD) patients may benefit from low-volume PEG given its efficacy and safety.^73,74 Novel oral sulfate tablets also show promise for this population.⁷⁵

Chronic kidney disease patients may tolerate PEG regimens safely, according to the available evidence.^76,77

Patients with chronic constipation may benefit from the potentially superior efficacy of OSP compared to PEG alone.⁴³ Strategies such as an extended low-residue diet, increased laxative volume, or adjuvants (e.g. lactulose and linaclotide) can further improve preparation. Combining low-volume PEG with linaclotide or lactulose enhances quality without increasing adverse events.^14,78,79

Diabetic patients may benefit from a comprehensive strategy, including reinforced education, a low-residue diet, hypoglycemic adjustment, and split-dose PEG.⁸⁰

Postcolorectal surgery patients may benefit from split-dose 4L PEG over single-dose 2L PEG.⁸¹ However, a low-volume PEG-bisacodyl combination appears equally effective as high-volume 4L PEG regimens.^82,83

During bowel preparation

The timing and regimen of bowel preparation should be tailored to the scheduled procedure time. Compared to the single-dose regimen, the split-dose regimen shows advantages in bowel cleanliness, sleep comfort and reduced symptoms.^84,85 while European Society of gastrointestinal endoscopy recommends an overnight split-dose regimen for elective colonoscopy, a same-day preparation is an acceptable alternative for afternoon procedures.⁸ The final dose should be initiated 4 to 6 hours and completed at least 2 hours before the colonoscopy.^72,86

Postbowel preparation

If the initial bowel preparation is inadequate, a repeat colonoscopy should be scheduled promptly with a reinforced preparation regimen. This may involve increasing the volume of cleansing solution, adding adjunctive agents, switching to a different laxative, or extending the period of a low-residue diet to ensure adequacy. Supplemental enema may be considered an effective rescue measure to avoid procedural delays in such cases.⁸⁷ Alternatively, administering additional oral laxatives on the same day may also serve as a practical and, in some instances, more effective alternative to enemas for achieving adequate cleansing.^88,89

To achieve high-quality bowel preparation, these steps need to be taken into account (Figure 1): (1) providing comprehensive patient education; (2) initiating a low-residue diet at least 1 day before the procedure; (3) selecting an appropriate bowel-cleansing regimen; (4) split-dose regimen and ensuring the last dose starts within 4 to 6 hours and ends at least 2 hours before colonoscopy; and (5) implementing a timely rescue strategy if initial preparation is suboptimal.

Figure 1.

How to achieve optimal bowel preparation.

Conclusion

In conclusion, high-quality bowel preparation is best achieved through a systematic, patient-centered strategy. Key elements include comprehensive patient education approach, timely dietary modification, and the selection of laxative regimens tailored to specific patient profiles and comorbidities. Such individualized bowel preparation strategies may improve cleansing quality and colonoscopy effectiveness, potentially leading to improved clinical outcomes and resource efficiency. However, the limitation is that the evidence of this narrative review presented lacks systematic quality assessment. Significant heterogeneity exists among the cited studies, and conclusions for certain patient subgroups are derived from limited or low-quality evidence, reflecting substantial uncertainty in these areas.

Footnotes

Acknowledgements

Figure support was provided by Figdraw. We have obtained the necessary permissions from copyright holders.

ORCID iD

Xin Gao

Informed consent

This review was approved by all authors.

Authors’ contributions

YW and XG contributed to the study concept and design, and drafting of the manuscript. MC contributed to revision of the manuscript. All authors reviewed the manuscript and approved the final manuscript.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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Strategies to optimize bowel preparation quality for colonoscopy in individuals

Abstract

Keywords

Introduction

Methods

The importance of bowel preparation

Epidemiology of CRC

Significance of colonoscopy

Importance of bowel preparation

Factors affecting the quality of bowel preparation

Bowel preparation quality scales

Individualized management of bowel preparation

Definition of individualized management

Why consider individualized bowel preparation management?

Specific measures of individualized management

Prebowel preparation

Patient education for bowel preparation

Laxatives

General patients

Specific patient groups

During bowel preparation

Postbowel preparation

Conclusion

Footnotes

Acknowledgements

ORCID iD

Informed consent

Authors’ contributions

Funding

Declaration of conflicting interests

References