Bowel screening
Exam Tips
- Know UK nation-specific programme details: England 50-74 every 2 years (FIT threshold 120 micrograms Hb/g); Scotland 50-74 (80 micrograms Hb/g); Wales 51-74 (initially 150 micrograms Hb/g, moving lower); Northern Ireland 60-74.
- After abnormal FIT, next step is specialist assessment and usually colonoscopy (or CT colonography if unsuitable), not repeat FIT as definitive triage.
- Normal screening FIT does not exclude cancer in symptomatic patients; symptoms override screening status.
- Adenoma risk stratification after colonoscopy determines recall versus surveillance/MDT review.
- Be ready to quote key harms numerically in viva/OSCE: false results and rare colonoscopy complications (major bleeding/perforation).
Definition
Bowel screening in the UK is a population-level cancer prevention and early detection programme using faecal immunochemical testing (FIT) in people without symptoms, followed by colonoscopy (or CT colonography if colonoscopy is unsuitable) when FIT is abnormal. Its clinical aim is to detect colorectal cancer earlier and identify/removal adenomatous polyps before malignant transformation, while balancing benefits against harms such as false results and procedure-related complications.
Pathophysiology
Screening targets occult lower gastrointestinal bleeding, a biological signal of colorectal neoplasia. Most colorectal cancers arise through the adenoma-carcinoma sequence, where progressive genetic/epigenetic change in colonic epithelium drives transition from normal mucosa to adenoma and then invasive carcinoma; FIT uses antibodies to human haemoglobin to detect microscopic blood loss from these lesions. Earlier-stage detection is associated with substantially better survival, and removal of premalignant adenomas reduces future cancer incidence. See Figure: adenoma-carcinoma sequence (core colorectal pathology diagram in standard GI pathology texts).
Risk Factors
- Increasing age (majority of colorectal cancers occur after age 60)
- Male sex
- Family history of colorectal cancer or inherited syndromes (e. g. Lynch syndrome, FAP)
- Personal history of adenomas or colorectal cancer
- Inflammatory bowel disease (ulcerative colitis or Crohn's colitis)
- Lifestyle factors: obesity, physical inactivity, smoking, high alcohol intake, high processed/red meat intake
- Socioeconomic deprivation (associated with worse stage-specific outcomes and survival)
Clinical Features
Symptoms
- Usually asymptomatic at time of invitation (screening population)
- If interval cancer develops: change in bowel habit, rectal bleeding, abdominal pain, unintentional weight loss, iron-deficiency anaemia symptoms
Signs
- Often no abnormal findings in screen-detected individuals
- Possible signs in undiagnosed colorectal pathology: pallor, abdominal or rectal mass, cachexia, positive digital rectal examination findings
Investigations
Management
Lifestyle Modifications
- Support informed uptake: explain benefits (earlier detection, prevention via polyp removal) and harms (false positives/negatives, overdiagnosis, colonoscopy risk).
- Encourage prompt GP review for alarm symptoms even with a recent negative FIT screening result (safety-netting for interval cancer).
- Promote colorectal risk reduction: smoking cessation, alcohol moderation, regular activity, healthy weight, higher fibre intake and lower processed/red meat intake.
Pharmacological Treatment
Bowel preparation before colonoscopy
- Macrogol 3350 compound oral powder (e. g. Klean-Prep): typically 4 sachets, each dissolved in 1 litre water, taken over several hours pre-procedure
- Macrogol with ascorbate oral solution (e. g. Moviprep): typically 2 litres total in split dosing (1 litre evening before, 1 litre on procedure day) plus extra clear fluids
- Sodium picosulfate with magnesium citrate oral powder (e. g. Picolax/Citrafleet): commonly 1 sachet then a second sachet 6-8 hours later (local protocol dependent)
No routine drug therapy is used for screening itself. Bowel-cleansing agents are protocol-driven; check local endoscopy instructions. Contraindications/cautions include suspected obstruction or perforation, toxic megacolon/severe active colitis, significant dehydration, severe renal impairment or heart failure (agent-specific), and electrolyte disturbance risk. Review medicines around colonoscopy (especially anticoagulants, antiplatelets, insulin, and SGLT2 inhibitors) per local safety protocol.
Surgical / Interventional
- Endoscopic polypectomy during colonoscopy for premalignant lesions
- Colorectal cancer cases are referred to MDT for definitive treatment (endoscopic, surgical, oncological, or combined pathways)
Complications
- False-positive FIT causing anxiety and unnecessary invasive investigation
- False-negative FIT with missed lesions and interval colorectal cancer
- Overdiagnosis/overtreatment of lesions with low biological risk
- Colonoscopy-related bleeding (higher with polypectomy)
- Colonoscopy-related perforation (rare but serious)
Prognosis
Screening improves outcomes primarily through stage shift and prevention: regular participation reduces bowel cancer mortality, and endoscopic removal of adenomas lowers incidence. UK data show markedly better 5-year survival for early-stage disease (around 90% for early localised disease) compared with metastatic presentation (around 10%), with persistent deprivation-related survival gaps.
Sources & References
✅NICE Guidelines(1)
- Bowel screening[overview]