01Role and principlesWho benefits and the main preventive aims.
Screening offers a test to an apparently well population to reduce colorectal-cancer mortality and detect precursor lesions. In England the NHS sends FIT every two years to registered people aged 50 to 74, with self-request available from age 75. A negative screen is time-limited and does not investigate new symptoms.
Surveillance is targeted follow-up after a defined risk lesion or condition. In BSG post-polypectomy guidance, an advanced adenoma is at least 10 mm or has high-grade dysplasia; an advanced serrated polyp is at least 10 mm or contains dysplasia. High risk means at least two premalignant polyps including one advanced lesion, or at least five premalignant polyps. Colonoscopy intervals also depend on hereditary genotype, colitis risk or previous colorectal cancer, and the index report must capture completeness, preparation and histology before an interval can be chosen.
Key points
- In England, people aged 50 to 74 registered with a GP are offered a home FIT kit every two years.
- People aged 75 or over can request a screening kit every two years through the NHS bowel-screening helpline.
- Screening applies to people without symptoms; rectal bleeding, bowel-habit change or anaemia require a diagnostic pathway.
- An abnormal screening FIT leads to specialist assessment and usually colonoscopy rather than a repeat kit for reassurance.
- High-risk post-polypectomy findings are at least five premalignant polyps, or at least two including an advanced adenoma (10 mm or larger or high-grade dysplasia) or advanced serrated polyp (10 mm or larger or any dysplasia); fit patients under 75 usually receive surveillance at three years.
- Hereditary syndromes, inflammatory bowel disease and previous cancer use separate specialist surveillance pathways.
02Assessment and patient selectionRisk features, eligibility and important cautions.
People registered with a GP are automatically sent a home FIT kit every two years from age 50 to 74; from 75 they can request a kit every two years.
An abnormal programme FIT leads to specialist screening practitioner assessment and usually colonoscopy if fit; repeating the home kit cannot safely cancel that assessment.
Current rectal bleeding, altered bowel habit, weight loss, anaemia or a mass needs a diagnostic pathway even after a recent negative screening result.
High risk means five or more premalignant polyps, or two or more with at least one advanced polyp; both number and advanced histology must be taken from a complete examination.
Lynch syndrome, familial adenomatous polyposis, colonic inflammatory bowel disease and previous colorectal cancer follow specialist protocols rather than average-risk screening intervals.
03Baseline assessmentMeasurements that guide the plan and track progress.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Screening FITFirst step - Why
- Detect occult human haemoglobin in an eligible asymptomatic population.
- Interpretation and limitations
- A programme-positive result triggers screening-centre assessment; the programme threshold differs conceptually from symptomatic FIT use.
- 02
Screening colonoscopy - Why
- Identify, biopsy and remove lesions after an abnormal screen.
- Interpretation and limitations
- Interpret the result with caecal completion, bowel preparation, polyp retrieval and histopathology.
- 03
Polyp histology - Why
- Classify adenoma, serrated lesion, dysplasia and completeness.
- Interpretation and limitations
- Number, size, morphology and histology determine whether surveillance is needed and at what interval.
- 04
Family-history and genetics assessment - Why
- Identify hereditary risk requiring gene-specific surveillance.
- Interpretation and limitations
- A vague family history is insufficient; record relatives, tumour type and age at diagnosis and refer appropriately.
04InterventionsLifestyle, treatment and escalation options.
01Worked case: symptoms appear during screeningMove an invited person into the symptomatic diagnostic pathwayFirst stepA 56-year-old receives an NHS screening FIT kit but develops six weeks of rectal bleeding, looser stool and 4 kg weight loss before returning it. They ask whether the postal screening sample is sufficient.+
- 1Explain that screening tests apparently well people and that the new symptoms require clinical assessment rather than waiting for a programme result.
- 2Check observations and ask about heavy bleeding and obstruction, then take a medicine and family history and perform abdominal and consented rectal examination.
- 3Issue a symptomatic quantitative FIT under NICE criteria if no direct-referral finding is present; record the symptom indication and create a task to review the numerical result.
- 4FIT returns 27 micrograms/g, so submit a suspected colorectal-cancer referral rather than handling it as a routine screening episode.
- 5Verify referral acceptance and completed colonoscopy. Biopsy confirms a rectal adenocarcinoma, prompting MRI and CT staging; document that screening administration has not duplicated or displaced this pathway.
02Abnormal population-screening FITComplete the programme assessment instead of repeating the kitAn asymptomatic 64-year-old receives an abnormal NHS bowel-screening FIT result and is invited to a specialist screening practitioner appointment. They are anxious and request a second home kit first.+
- 1Explain that faecal blood raises risk but is not itself a cancer diagnosis, and that intermittent bleeding makes a repeat kit an unsafe way to cancel assessment.
- 2At the specialist screening practitioner review, assess comorbidity, medicines, bowel preparation, sedation and capacity for colonoscopy and discuss CT colonography if colonoscopy is unsuitable.
- 3Proceed with programme colonoscopy when fit. Record caecal completion, cleansing quality, every polyp and retrieval; send removed lesions for histology.
- 4Verify the final diagnosis and follow-up route. A completely excised 8 mm low-grade tubular adenoma without other premalignant polyps does not by itself meet the high-risk surveillance criteria; return to screening as advised by the programme.
03High-risk post-polypectomy findingsUse the whole index examination to assign the intervalA complete, well-prepared colonoscopy removes six premalignant polyps, all retrieved and completely excised; the patient is 68 and fit for surveillance.+
- 1Reconcile the endoscopy map with histology, including total premalignant-polyp count, size, serrated versus adenomatous type, dysplasia and completeness of excision.
- 2Recognise that five or more premalignant polyps meets the BSG/ACPGBI/PHE high-risk criterion even if none is individually advanced.
- 3Recommend a surveillance colonoscopy after three years for this fit patient under 75, documenting the bowel-preparation and completion evidence that supports the decision.
- 4Verify booking and histology communication; re-evaluate the plan if genetic features, limited life expectancy or a separately indicated hereditary or colitis protocol applies.
05Targets, monitoring and follow-upResponse, safety and longer-term review.
- Track return and results of programme kits while recognising that a missed kit is not a negative test.
- After screening colonoscopy, reconcile endoscopy findings with histology before assigning any surveillance interval.
- Confirm patients with hereditary or colitis risk have entered the correct specialist programme.
- Continue symptom safety-netting after a negative screen because interval cancers and non-bleeding lesions can occur.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Screening is not diagnosis
A screening interval cannot be used to defer assessment of current bleeding, bowel-habit change, weight loss or iron deficiency.
Programme thresholds have purpose
Screening and symptomatic FIT operate in different pre-test populations and should not be interchanged without explanation.
Quality affects interval
An incompletely examined or poorly prepared colon cannot support the same surveillance decision as a high-quality complete test.
Participation needs access
Address language, disability, address instability and practical sampling barriers so an offered kit becomes a usable opportunity.
07Common pitfallsFrequent interpretation and management errors.
- 01
Telling a symptomatic person to wait for routine screening can delay diagnosis despite apparent programme eligibility.
- 02
Repeating a positive screening FIT instead of completing assessment risks false reassurance from intermittent bleeding.
- 03
Choosing surveillance from polyp size alone ignores number, histology, excision and examination quality.
- 04
Applying average-risk screening to Lynch syndrome or longstanding colitis leaves inherited or inflammatory risk undertreated.