01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Change in bowel habit becomes clinically useful only when baseline and new stool form, frequency, urgency, evacuation and duration are described. Abrupt watery diarrhoea after antibiotics, gradual narrowing with weight loss, and small liquid overflow around faecal impaction carry different mechanisms and priorities.
The examination seeks dehydration, distension, mass, tenderness, peritonism and rectal loading. FIT can stratify colorectal-cancer risk in stable symptomatic adults, while progressive obstruction features require emergency imaging and surgical review rather than completion of an outpatient test sequence.
Key points
- Define baseline stool form and frequency, then record the exact new pattern and its duration.
- Vomiting, distension and inability to pass stool or flatus suggest obstruction and need emergency assessment.
- Weight loss, rectal bleeding, iron deficiency or an abdominal or rectal mass increase cancer concern.
- Offer quantitative FIT for unexplained change in bowel habit under current NICE guidance.
- Tenesmus and frequent small stools prompt rectal assessment but do not exclude proximal colonic disease.
- Review every result and reopen the differential when symptoms persist after negative structural testing.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Structural colorectal disease
Cancer, stricture, diverticular narrowing and large polyps can alter calibre, transit or evacuation, sometimes progressing toward obstruction.
Functional and inflammatory causes
Irritable bowel syndrome, inflammatory bowel disease, infection, medication and endocrine or malabsorptive disorders can change frequency and consistency.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Luminal narrowing
A tumour or stricture restricts passage, causing altered calibre, incomplete evacuation and eventually upstream dilatation as colonic contents accumulate proximally.
- 2Mucosal inflammation
Inflammation impairs water absorption and produces urgency, mucus, bleeding and nocturnal stooling through exudation and accelerated transit.
- 3Transit disturbance
Drugs, diet, autonomic changes and functional gut-brain mechanisms can accelerate or slow colonic transit without a fixed obstruction.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Define the patient's baseline, the exact change and its duration; alternating labels such as diarrhoea and constipation are unhelpful until stool form, frequency and incomplete evacuation are described.
Unintentional weight loss, rectal bleeding, iron-deficiency anaemia, an abdominal or rectal mass and persistent unexplained symptoms increase concern for malignancy.
New loose stool can represent overflow around faecal loading, medication effects, infection, inflammation or malabsorption rather than a single disease category.
Tenesmus, urgency, mucus and small frequent stools may indicate rectal inflammation or a space-occupying lesion and should prompt anorectal assessment.
A family history should record which relative, cancer type and age at diagnosis because vague statements about bowel problems do not establish hereditary risk.
05InvestigationsWhat to request, why it matters and how to interpret it.
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
Focused abdominal and digital rectal examinationFirst step - Why
- look for distension, mass, tenderness, faecal loading and low rectal pathology
- Interpretation and limitations
- Normal findings reduce neither proximal pathology nor intermittent obstruction to zero; relate them to symptom trajectory.
- 02
Full blood count, ferritin, inflammatory markers and renal profile - Why
- seek anaemia, inflammation, dehydration and treatment-relevant organ dysfunction
- Interpretation and limitations
- Normal tests do not exclude early colorectal cancer, while inflammatory abnormalities are non-specific.
- 03
Quantitative faecal immunochemical test - Why
- stratify symptomatic colorectal-cancer risk under NICE recommendations
- Interpretation and limitations
- A result at or above the pathway threshold supports urgent referral; below-threshold results still require review if symptoms persist or clinical concern is strong.
- 04
Colonic imaging or endoscopy - Why
- define mucosal or structural disease when the pathway indicates definitive investigation
- Interpretation and limitations
- Colonoscopy allows biopsy; CT colonography shows the whole colon but cannot remove lesions and may generate extracolonic findings.
- 05
Stool studies or faecal calprotectin selected by context - Why
- investigate infection or inflammatory disease when loose stool is prominent
- Interpretation and limitations
- Order targeted assays rather than indiscriminate panels and interpret calprotectin alongside age, medicines and cancer risk.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Faecal impaction with overflow
Rectal loading, reduced mobility and constipating drugs support overflow, but proximal obstruction must still be considered.
Irritable bowel syndrome
Recurrent pain related to defaecation with a chronic pattern may fit IBS only after red flags and appropriate tests are addressed.
Infective diarrhoea
Abrupt onset, exposure history and systemic symptoms favour infection rather than a slowly progressive neoplastic process.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked case: applied change in bowel habit and alarm featuresReach a specific decision and confirm it happenedFirst stepA 67-year-old has six weeks of progressively looser stool, urgency and 4 kg weight loss. There is no mass or obstruction on examination, haemoglobin is 116 g/L and quantitative FIT returns 16 micrograms haemoglobin per gram.+
- 1Confirm stable physiology and ask directly about vomiting, progressive distension and passage of flatus; their absence makes immediate obstruction less likely in this case.
- 2Establish that the looser stool is a six-week change from baseline and document urgency, nocturnal symptoms, blood, pain, appetite, weight, medicines, travel and family history.
- 3Examine the abdomen and rectum for a mass, tenderness, distension or loading, and send full blood count and ferritin to identify anaemia alongside selected baseline tests.
- 4Interpret 16 micrograms per gram as above the NICE threshold and submit a suspected colorectal-cancer referral that includes weight loss, symptom duration, examination and blood results.
- 5Flexible sigmoidoscopy finds a mid-rectal tumour and biopsy confirms adenocarcinoma. Verify pelvic MRI, CT staging and colorectal multidisciplinary review rather than treating the FIT result as the endpoint.
02Stable below-threshold reviewResolve symptoms that persist after a low FITA 54-year-old has new looser stool for seven weeks, FIT 4 micrograms per gram, no mass or anaemia, but symptoms remain unexplained at the first review.+
- 1Check sample completion and the exact numerical FIT, repeat abdominal and rectal examination and review medicines, weight, inflammatory markers and coeliac testing.
- 2Use the persistent trajectory and local lower-GI pathway to decide on non-cancer colorectal or gastroenterology investigation; do not repeat FIT indefinitely in place of diagnosis.
- 3Verify whether symptoms resolve or structural and mucosal tests are completed, with a new urgent referral if bleeding, iron deficiency, weight loss or a mass appears.
03Acute obstruction pathwayTreat bowel obstruction before outpatient alarm-feature testingA 73-year-old has progressive distension, colicky pain, faeculent vomiting and has passed neither stool nor flatus for 36 hours; pulse is 118/min and creatinine has risen.+
- 1Begin ABCDE care, keep nil by mouth, establish intravenous access, correct fluid and electrolyte deficits, monitor urine and use nasogastric decompression for persistent vomiting.
- 2Obtain urgent contrast CT to identify transition point, tumour, volvulus, caecal diameter, closed-loop features, ischaemia or perforation; FIT and routine proctoscopy cannot answer this emergency question.
- 3Involve colorectal surgery and anaesthesia while resuscitation continues and decide on stent, diversion or resection according to site, perforation risk, stage and physiological reserve.
- 4DefinitiveVerify decompression, pain, lactate, renal recovery and definitive pathology, and arrange completion of unexamined colon when safe.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Large-bowel obstruction
Progressive narrowing may cause distension, vomiting, electrolyte disturbance, ischaemia and perforation if decompression and source control are delayed.
Diagnostic delay
Normalising a persistent new pattern can defer investigation until disease is more advanced and resection becomes more extensive.
Nutritional and fluid consequences
Prolonged diarrhoea or poor intake may cause dehydration, weight loss and micronutrient deficiency that impair resilience before treatment.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Ask the patient to report obstruction features, heavy bleeding, syncope or rapid deterioration immediately rather than waiting for a routine appointment.
- Review the actual FIT value and laboratory pattern, not merely whether a test is marked normal by the electronic system.
- Confirm attendance and outcome of colorectal investigation, including biopsy results and any plan for incomplete colonoscopy.
- Revisit the differential after negative structural testing when symptoms continue, considering inflammatory, malabsorptive, medication and functional causes.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Baseline gives meaning
Three stools daily may be normal for one person and a major change for another; comparison with the established pattern makes the symptom clinically interpretable.
Rectal symptoms localise imperfectly
Tenesmus and urgency focus attention on the rectum but do not exclude more proximal colonic disease or a diffuse inflammatory process.
Overflow can look like diarrhoea
Liquid stool passing around impaction is particularly relevant in frail or neurologically impaired people and changes initial management.
Negative testing needs ownership
A low-risk result is useful only when someone reviews persistence, resolves discordant alarm features and documents the next step.
11Common pitfallsFrequent interpretation and management errors.
- 01
Recording change in bowel habit without describing stool form, frequency or duration prevents meaningful risk assessment.
- 02
Assuming constipation is benign in the presence of progressive distension, vomiting or absolute obstipation can miss obstruction.
- 03
Using a negative FIT as an endpoint despite persistent alarm features creates a gap between triage and diagnosis.
- 04
Ordering broad stool tests without a clinical question can distract from colorectal cancer assessment in an older adult.