Colonoscopy Prep: How to Properly Clear Your Colon
Patient Guide · Silo Endoscopy · Colombia 2026
Preparation for colonoscopy: how to properly clear the colon
A colonoscopy with inadequate preparation may need to be repeated or may miss important lesions. This guide explains exactly how to prepare the colon — diet, laxative, timing, and why split-dose preparation works better
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GSMED Imaging medical team — digestive endoscopy Colombia
Based on: ESGE Guidelines on Bowel Preparation for Colonoscopy 2023, ASGE Bowel Preparation Quality 2024, Martel 2023 meta-analysis, and colonoscopy practice in leading Colombian centers.
Bowel preparation is, without question, the factor that most influences the quality of a colonoscopy — more than the brand of the endoscope or the experience of the endoscopist. Excellent preparation allows even 2–3 mm polyps to be seen with complete clarity; inadequate preparation can cause 1 cm lesions to go completely unnoticed under fecal residue. This guide explains exactly how to do it right.
1. The preparatory diet — the day before
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Clear liquid diet the day before (standard)
The traditional standard: only clear liquids (fat-free broth, water, clear gelatin, pulp-free apple juice, clear isotonic drinks) all day before. No solids of any kind. Effective but uncomfortable due to hunger and poorly tolerated by some patients — especially diabetics who cannot skip carbohydrates.
→ Traditional standard · Uncomfortable · One day of solid food fasting
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Low-fiber diet (validated alternative)
The low-fiber diet the day before (white rice, chicken, egg, white bread — no fruit, vegetables, or dairy) has comparable evidence to the liquid diet in preparation quality according to the Martel 2023 meta-analysis, with greater patient tolerance. Many centers offer it as an alternative to improve adherence — especially in diabetic or elderly patients.
→ Same effectiveness as liquids · Greater tolerance · Diabetics and elderly
2. Laxatives available in Colombia
| Laxative | Volume | Advantage | Limitation |
|---|---|---|---|
| Polyethylene glycol (PEG) 4L | 4 liters | High effectiveness · No absorption · Safe in CKD and CHF | High volume — difficult tolerance · Bad taste |
| PEG 2L + bisacodyl or ascorbic | 2 liters | Lower volume · Same effectiveness as 4L · More tolerable | Do not use in advanced CKD · Contraindicated in stenosis |
| Sodium picosulfate + MgCitrate (PICOPREP) | 2 doses of 150 mL + water | Very low volume · Very well tolerated · Pleasant taste | Contraindicated in severe CHF and advanced CKD · Higher risk of dehydration |
| Sodium phosphate | Tablets | Very little volume | Contraindicated in CKD, CHF, elderly, hypertension — documented nephrotoxicity. AVOID. |
3. Split-dose preparation — why it is better
Split-dose preparation is the standard of care according to ESGE 2023
Split-dose preparation consists of taking half the laxative the afternoon before and the other half the morning of the procedure (at least 2 hours before the colonoscopy). ESGE 2023 recommends it as the first choice over same-day preparation for two reasons: (1) better quality of preparation of the right colon — the right colon clears better the less time has passed since the last dose; (2) greater patient tolerance — two smaller doses are better tolerated than one large dose at once. If the colonoscopy is in the morning: first dose at 6–8 PM the day before, second dose at 6–7 AM on the day of the procedure.
4. Special situations that change the preparation
- Diabetic patients: the liquid diet can cause blood sugar imbalance. The low-fiber diet the day before + adjustment of antidiabetics with the treating physician is the safest option.
- Patients with chronic kidney disease: avoid sodium phosphate and PEG with ascorbic acid. PEG 4L without additives is the safest. Supplemental IV hydration may be necessary in advanced CKD.
- Patients on anticoagulants: bowel preparation itself does not require suspending anticoagulation. Suspension depends on whether polypectomy or biopsy is planned — consult with the physician who prescribed the anticoagulant.
- Severe constipation: may require a 3-day preparation with a low-residue diet + mild oral laxative before starting the standard protocol.
Can I take my regular pills on the day of the colonoscopy?
The general rule is: yes, with a small sip of water, for essential medications. The most important ones not to interrupt are antihypertensives, antiepileptics, and anticoagulants when your doctor has indicated continuing them. There are exceptions: metformin is generally suspended 24–48h if iodinated contrast is going to be used (if there is no CT that day, it can be taken), and oral antidiabetics must be adjusted if the fast is prolonged. Always consult with your doctor about specific questions about your medication.
High-definition colonoscopy systems available in Colombia — GSMED
Olympus, Pentax, and Fujifilm colonoscopes with magnified imaging for maximum lesion detection — local technical support.
Related articles
Sources
- ESGE. Bowel preparation for colonoscopy. esge.com. 2023. Split-dose, laxatives. ESGE 2023
- ASGE. Bowel preparation quality — standards. asge.org. 2024. ASGE 2024
- Martel M et al. Low-residue diet vs clear-liquid diet — meta-analysis. Endoscopy. 2023. Martel 2023
