Colonoscopy Explained: Screening, Polyps, Preparation and Recovery
Colonoscopy is the reference standard for colorectal cancer screening. Learn who to screen from age 45, bowel prep, and polyp surveillance.
Colonoscopy is the reference standard for colorectal cancer detection and prevention — polyps can be removed during the same procedure. USPSTF (2021) recommends screening in average-risk adults from age 45–75. NHS bowel cancer screening uses FIT (faecal immunochemical test) first, with colonoscopy for positive results. Polyp size, number, and histology determine surveillance intervals.
Colonoscopy allows direct visualisation of the entire colon plus polyp removal in one procedure — dropping colorectal cancer incidence by up to 40% and mortality by ~50% (long-term follow-up studies). USPSTF (2021) lowered the screening age to 45 based on rising early-onset colorectal cancer, screening biennially or every 10 years depending on modality. The NHS bowel cancer screening programme uses FIT (age 54–74, moving to 50–74) with colonoscopy for FIT-positive results. High-quality colonoscopy targets: adenoma detection rate ≥ 25%, caecal intubation ≥ 95%, withdrawal time ≥ 6 minutes, split-dose bowel prep. BSG/ACPGBI 2020 UK polyp surveillance: high-risk (≥ 2 premalignant polyps of any size, ≥ 5 mm serrated polyps, or family history) → 3-year colonoscopy; low-risk → 5-year FIT. US Multi-Society Task Force 2020 uses similar risk stratification. Modern polyps removed by EMR/ESD (endoscopic mucosal / submucosal resection) can spare surgery in early cancers. Colon capsule endoscopy is emerging for incomplete or contraindicated colonoscopy.
- Screening age
- USPSTF 45–75; NHS FIT then colonoscopy
- Bowel prep
- Split-dose PEG or macrogol
- Adenoma detection rate
- ≥ 25% (quality target)
- Perforation risk
- ~1 in 1000
- Bleeding after polypectomy
- ~1–2%
Polyp surveillance intervals (BSG/ACPGBI 2020)
| Finding | Next test |
|---|---|
| Complete high-quality colonoscopy, no polyps or 1 small adenoma | 10 years |
| 1–2 premalignant polyps < 10 mm | FIT/no action or 5 y |
| ≥ 2 premalignant polyps ≥ 10 mm, or ≥ 5 polyps < 10 mm | 3 years |
| Sessile serrated polyp ≥ 10 mm or dysplastic | 3 years |
| Family history HNPCC/Lynch | Every 1–2 years |
Preparation
Low-residue diet 2–3 days before; clear fluids the day before.
Split-dose bowel prep (half the evening before, half in the early morning) improves right-colon cleansing.
Stop iron and constipating drugs 5 days before if possible.
Anticoagulation and antiplatelet plans arranged with the endoscopy service — do not stop without advice.
- Rectal bleeding + iron-deficiency anaemia — urgent 2-week referral, not FIT screening.
- Persistent change in bowel habit + weight loss — urgent referral pathway.
- Post-colonoscopy: severe abdominal pain, fever, or heavy PR bleeding — emergency.
Colonoscopy pathway
- 1FIT positive or symptoms?Colonoscopy.
- 2Polyp found?Removed and sent for histology.
- 3High-risk polyps?Surveillance colonoscopy 3 y.
- 4Low-risk polyps?Return to FIT or 5-y surveillance.
Related questions people ask
Frequently asked questions
- Colonoscopy detects and removes precancerous polyps.
- Screening age lowered to 45 in the US in 2021.
- Bowel prep quality is the biggest determinant of accuracy.
- Polyp surveillance intervals depend on risk category.
- Symptoms bypass screening pathways — refer urgently.
References
2 sources- USPSTFColorectal Cancer Screening 2021
US Preventive Services Task Force.
uspreventiveservicestaskforce.org
- BSG/ACPGBIPost-Polypectomy Colonoscopy Surveillance Guidelines
UK guideline.
gut.bmj.com
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