Optimizing bowel preparation in high-risk patients undergoing colonoscopy

Poor bowel preparation undermines colorectal cancer (CRC) screening. High‑risk patients—obese, diabetic, opioid users, former smokers—often have comorbidity, medication, and sociodemographic factors causing suboptimal preparation despite adherence. Inadequate preparation causes missed lesions, longer procedures, and higher costs. PEG solutions are preferred for safety in renal or cardiac disease. Split‑dose PEG with a low‑residue diet is recommended. Tailored regimens help chronic constipation, opioid dependence, and diabetes. Education, navigators, and reminders improve compliance. Adjuncts include bisacodyl; sodium phosphate should be avoided in the elderly or renally impaired. Open‑access colonoscopy has expanded post‑COVID‑19. This review summarizes risk factors and practical strategies.

Introduction

CRC is the third leading cause of cancer death in the US and second worldwide. Colonoscopy reduces CRC mortality by up to 68% and incidence by up to 60% through detection and removal of premalignant lesions. Its efficacy depends on preparation quality. Inadequate preparation causes missed polyps, repeat colonoscopies, delayed care, higher costs, and reduced capacity. High‑risk groups include older adults, obese patients, those with immobility, smoking, neuromuscular disease, diabetes, chronic constipation, renal insufficiency, cirrhosis, prior stroke, and users of motility‑slowing medications. These risks often cluster, so tailored regimens and adherence support are needed.

Determinants

Physiologic/comorbidity: Obesity slows transit. Diabetes causes autonomic dysfunction and gastroparesis. Chronic constipation increases stool burden and reduces purgative efficacy.

Medications: Opioids reduce motility. Tricyclic antidepressants strongly associate with inadequate preparation (OR 3.85); SSRIs show a weaker association (OR 1.69). Diuretics and antihypertensives may cause dehydration and interfere with purgation.

Psychosocial: Older age, limited health literacy, language barriers, and low socioeconomic status reduce adherence. Anxiety, fear, and embarrassment may discourage completion. Taste, volume, and side effects can overwhelm patients.

Prior inadequate preparation: The strongest predictor of future inadequacy (OR 1.92). Prevention through tailored education at the first encounter is essential.

Consequences

Missed lesions: On the Boston Bowel Preparation Scale (BBPS), inadequate preparation is any segment scoring 0–1 or total <5. Poorly prepared segments had adenoma detection rates as low as 3% versus 11% in well‑prepared segments. After inadequate initial examination, per‑adenoma miss rates were 69% and advanced adenoma miss rates 60%; all CRCs found on repeat colonoscopy were missed initially. Serrated polyp miss rates reached 84%. Even BBPS = 1 segments had increased miss rates, supporting repeat colonoscopy when any segment scores below 2.

Procedure time/complications: Poor visualization makes cecal intubation harder. Longer cecal intubation times associate with reduced adenoma detection, though longer withdrawal may offset this. Larger polyp resection increases time and bleeding risk; evidence linking longer procedural time alone to adverse outcomes is limited.

Costs: Colonoscopy is not cost‑effective when more than 13% of procedures require repeat colonoscopy due to poor preparation. Repeat rates range from 24.5% (UK) to 63% (Spain).

Outcomes: Fair, poor, and insufficient preparation associate with higher CRC mortality; 10‑year CRC mortality rose from 0.14% with good/excellent preparation to 0.41% with suboptimal preparation. In Lynch syndrome, adequate preparation more than doubled the odds of adenoma detection.

Evidence‑Based Regimens

Standard options: High‑volume PEG‑electrolyte lavage solutions (PEG‑ELS; GoLYTELY, CoLyte) are isotonic and safe in renal or cardiac disease, but 4 L hinders tolerability. Split‑dose (2 L evening before, 2 L morning of) improves proximal cleansing by ~30% and polyp detection; meta‑analysis showed improved satisfactory preparations (OR 3.70) and willingness to repeat (OR 1.76). Sulfate‑free PEG‑ELS have comparable efficacy with less metallic taste but still require 4 L.

Low‑volume PEG‑based regimens (MoviPrep 2 L; PLENVU 1 L with high‑dose ascorbate) improve tolerability but may still cause nausea and bloating. Oral sulfate preparations (SUPREP, SUTAB) use 12–24 oz purgative plus 2–2.5 L clear liquids; they are hypertonic and should be avoided in renal insufficiency, heart failure, or electrolyte disturbances. Sodium picosulfate (CLENPIQ) and sodium phosphate tablets (OsmoPrep) are effective but risk volume depletion and electrolyte derangement; avoid in CKD, bowel obstruction, or heart failure.

Non‑FDA‑approved MiraLAX/Gatorade (238 g PEG‑3350 in 2 L sports drink) is hypotonic, better tolerated, and achieves comparable cleanliness when used in sufficiently large amounts, with minimal laboratory derangements. Magnesium citrate and bisacodyl are common adjuncts.

High‑risk strategies: The AGA and US Multi‑Society Task Force recommend split‑dose 4‑L PEG‑ELS plus 15 mg bisacodyl after a 2–3 day low‑residue diet and clear liquids the day before colonoscopy. For renal insufficiency or cardiac disease, isotonic low‑volume PEG solutions minimize fluid and electrolyte shifts. For patients unable to tolerate high volumes, low‑volume ascorbate regimens (MoviPrep, PLENVU) are reasonable alternatives.

Adjuncts: Bisacodyl enhances peristalsis and reduces volume needed; contraindicated in ileus, obstruction, severe dehydration, or acute inflammatory disease. Sodium picosulfate with magnesium citrate enhances efficacy; avoid in renal insufficiency. Magnesium citrate is contraindicated in renal insufficiency due to hypermagnesaemia risk. Simethicone reduces bloating and gas. Metoclopramide improves gastric emptying but may cause extrapyramidal symptoms and is not routinely used. Loperamide is generally contraindicated during preparation, but when used after completing lavage it improved cecal cleansing (2.0% vs. 12.7% dirty/bile‑coated cecum) without delaying the first bowel movement. Peripherally acting μ‑opioid receptor antagonists (methylnaltrexone, naloxegol) help opioid‑induced constipation while preserving analgesia; contraindicated in mechanical obstruction.

Non‑pharmacologic adjuncts: Double preparation improves adequate cleansing and polyp detection. MiraLAX‑PEG may be used for patients who struggle with high volumes or are at risk of fluid overload. Dietary fiber (psyllium >10 g/day for ≥4 weeks) improves stool frequency and consistency, especially in chronic constipation, but may need combination with osmotic or stimulant laxatives. A low‑residue diet for 2–3 days before the procedure with a split‑dose purgative has better compliance and comparable or superior cleansing versus clear liquids, with improved satisfaction and less hunger, nausea, and bloating.

Educational and Supportive Interventions

Oral and written instructions: The AGA recommends combined verbal and written instructions covering all aspects of preparation. Standardized formats—booklets, animated videos, infographics—are effective when tailored to health literacy and language. Combining written instructions with video‑based education is independently associated with adequate preparation quality.

Audiovisual tools: A randomized trial found smartphone‑delivered audiovisual re‑education significantly improved mean BBPS scores (7.53 vs. 6.29) and adherence. Virtual reality video education resulted in higher BBPS scores (7.61 vs. 7.04) and higher adenoma detection rates (32.6% vs. 22.1%), though cost and scalability remain uncertain.

Patient navigation: Navigators provide individualized education, review protocols, and ensure understanding. Navigated patients were 5.9 times more likely to achieve adequate preparation. Navigation reduced missed appointments (0% vs. 15.6%) and cancellations within 24 h. Navigation addresses logistical, sociodemographic, and psychosocial barriers and has improved completion among Hispanic patients and eliminated gender disparities.

Open‑Access Colonoscopy

Open‑access colonoscopy (OAC) allows primary care physicians to refer directly without a pre‑procedure gastroenterology consultation. Expanded after COVID‑19 to address backlogs, OAC improves access for underserved communities. However, OAC is associated with higher rates of inadequate preparation, incomplete procedures, and inappropriate screening intervals. A key driver is the absence of direct gastroenterologist‑patient interaction for detailed instructions and risk assessment. Referring PCPs may lack familiarity with preparation nuances in high‑risk patients. Research on preparation education quality in OAC settings is lacking.

Improvement strategies: Improve communication between referring PCPs and gastroenterology teams; integrate standardized protocols with culturally tailored written materials, videos, and mobile applications; include patient navigators; and establish a feedback loop notifying primary care teams of inadequate preparations.

Future Directions

Patient‑related barriers remain dominant. Patient navigator programs and digital health interventions (SMS reminders) show promise for improving adherence and reducing no‑shows. Research is needed on MiraLAX‑Gatorade as an alternative to high‑volume PEG, standardized dosing protocols for non‑FDA‑approved PEG + Gatorade, and post‑lavage loperamide to improve mucosal visualization—though not currently recommended by the US Multi‑Society Task Force, with concerns about adherence, side effects, and cost‑effectiveness.

Conclusions

Adequate bowel preparation is essential for effective CRC screening but remains challenging in high‑risk patients. Inadequate preparation reduces lesion detection, increases procedural complexity and costs, and worsens outcomes. Optimizing preparation requires an individualized, patient‑centered, multifactorial approach. Evidence supports tailored regimens, dietary modifications, adjunctive pharmacologic agents, and structured patient education to improve preparation quality and adherence, enhancing colonoscopy quality and maximizing the preventive impact of CRC screening.

Full text

https://www.xiahepublishing.com/2994-8754/JTG-2025-00051

The study was recently published in the Journal of Translational Gastroenterology.

Journal of Translational Gastroenterology (JTG) dedicates to improving clinical diagnosis and treatment, advancing understanding of the molecular mechanisms, and promoting translation from bench to bedside of gastrointestinal, hepatobiliary, and pancreatic diseases. The aim of JTG is to provide a forum for the exchange of ideas and concepts on basic, translational, and clinical aspects of gastroenterology, and promote cross-disciplinary research and collaboration.

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