Constipation Algorithm

Safety

Red Flags — Screen for serious pathology before assuming functional constipation

Screened — no red flags identified

Any of the following → urgent action required. Do not manage as simple constipation until excluded.

Rectal bleeding (bright red / dark) Especially if unprovoked, mixed with stool, or with altered stool → FIT first (NICE NG12, updated April 2026: rectal bleeding with abdominal pain or weight loss under 50; unexplained rectal bleeding at 50 or over) → suspected cancer pathway referral if FIT ≥10 µg Hb/g. A positive FIT triggers the urgent referral pathway. Do not delay referral because FIT is negative, unavailable or not returned when there is strong clinical concern, persistent unexplained symptoms, a mass or an anal ulcer. Rectal mass, or unexplained anal mass or anal ulcer → consider a suspected cancer pathway referral without waiting for FIT. Severe bleeding, haemodynamic compromise or suspected acute pathology → emergency assessment, not FIT

Unintentional, unexplained weight loss Quantify it and assess in context. NICE lower-GI FIT criteria depend on age and the presence of abdominal pain or other symptoms (weight loss at 50 or over, or at 40 or over with abdominal pain) — there is no general NG12 requirement for ≥5% weight loss → colorectal suspected cancer pathway if FIT ≥10 µg Hb/g. Check FBC and iron studies, usually including ferritin; interpret ferritin with CRP/inflammation where relevant. CEA is not a diagnostic test

Persistent change in bowel habit Any age, new looser stools or constipation → FIT → colorectal suspected cancer pathway referral if ≥10 µg Hb/g (NICE NG12)

Iron-deficiency anaemia Confirm iron deficiency with ferritin, supported by transferrin saturation or other iron studies where inflammation may make ferritin falsely normal. Request coeliac serology and FIT according to the current local pathway (BSG/ACPGBI 2025: FIT guides, not replaces, investigation). In men and postmenopausal women with confirmed unexplained IDA, a negative FIT does not by itself remove the need for appropriate upper and lower GI assessment (BSG 2021)

Abdominal / rectal mass Suspected cancer Palpable mass → rectal mass: consider a colorectal suspected cancer pathway referral without waiting for FIT; unexplained anal mass/ulcer: consider an anal suspected cancer pathway referral; abdominal mass: offer FIT, but do not let FIT delay referral when concern is strong — consider a suspected cancer pathway referral (NICE HTG690) — same-day assessment if obstruction or severe pain

Acute intestinal obstruction Absolute constipation + vomiting + distension + no flatus → same-day (urgent) hospital assessment; call 999 if unstable or cannot be safely transported. Bowel sounds neither confirm nor exclude obstruction

Neurological symptoms Immediate emergency assessment for new urinary retention, saddle anaesthesia, bilateral leg weakness or rapidly progressive neurological deficit suggestive of cauda equina syndrome

Severe pain / peritonism Suspected obstruction, perforation, volvulus, peritonitis, shock or severe uncontrolled pain → same-day (urgent) hospital assessment; call 999 if unstable or cannot be safely transported. Bowel sounds neither confirm nor exclude obstruction

New constipation in an older adult Requires careful assessment and usually FIT if it represents an unexplained change in bowel habit. Age alone does not mandate a suspected cancer referral. Escalate according to FIT, bleeding, anaemia, weight loss, mass, pain, obstruction or persistence. FIT is not needed for short-lived constipation with an obvious cause

Family history Lynch syndrome / FAP Take a three-generation family history where there is concern about hereditary colorectal cancer. Refer for genetic or specialist assessment according to the local hereditary-cancer pathway. FIT does not replace genetic risk assessment or specialist referral — a positive FIT is not the only reason to refer

Clozapine with bowel symptoms Constipation with abdominal pain, distension, vomiting, overflow diarrhoea or systemic illness → same-day urgent medical assessment; do not wait several days before escalating (risk of ileus, obstruction, bowel ischaemia and death)

NICE NG12 offers FIT for a change in bowel habit or iron-deficiency anaemia at any age, an abdominal mass, unexplained weight loss and abdominal pain at 40+, rectal bleeding with abdominal pain or weight loss under 50, unexplained rectal bleeding, abdominal pain or weight loss at 50+, and anaemia without iron deficiency at 60+ — with a suspected cancer pathway referral if FIT is ≥10 µg Hb/g; a rectal mass, or an unexplained anal mass or anal ulceration, is considered for a suspected cancer pathway referral without waiting for FIT. Safety-net and do not delay referral when strong concern persists despite a FIT below threshold or no returned sample. Early diagnosis is the biggest determinant of colorectal cancer survival. Missing a palpable mass or saddle anaesthesia can result in irreversible harm — cauda equina decompression must occur within hours. Volvulus and obstruction are time-critical.

Diagnose

Confirm constipation — Use Rome IV criteria and Bristol Stool Chart

Diagnosis confirmed with criteria

Constipation is a symptom-based diagnosis. Rome IV (≥2 criteria for ≥3 months, onset ≥6 months ago) helps with chronic functional constipation — it is not a prerequisite for managing a first presentation once red flags and secondary causes are considered. Do not apply it as a reassurance tool before assessing red flags, medication causes and secondary pathology, and do not diagnose functional constipation if IBS-C is more appropriate or another cause is identified.

Rome IV Criteria

≥2 of: <3 stools/week · straining >25% of defaecations · lumpy/hard stools (BSC 1–2) >25% · sensation of incomplete evacuation >25% · sensation of anorectal blockage >25% · manual manoeuvres >25%

Bristol Stool Chart

Types 1–2 = constipated · Types 3–4 = normal · Types 5–7 = loose/diarrhoea. Ask patient to identify their typical stool type

Key history questions

Onset, frequency, consistency, straining, blood, mucus, pain, diet change, new medications, obstetric history (women), systemic symptoms

Medication review

Opioids, iron supplements, calcium channel blockers (verapamil), antidepressants (TCAs), antipsychotics, antihistamines, anticholinergics — all cause constipation. Ask specifically about clozapine: constipation can progress rapidly to ileus, obstruction and death — treat proactively; pain, distension, vomiting or overflow → same-day urgent medical assessment (SPS)

Baseline severity

Use Patient Assessment of Constipation Symptoms (PAC-SYM) or ask: "How many days per week do you open your bowels?" to track response to treatment

Rome IV criteria standardise diagnosis and avoid over-medicalising normal variation. Many patients with ≤3 stools/week feel fine — it's the symptom burden that matters. Medication-induced constipation is common and often reversible. Establishing a baseline enables you to assess treatment response objectively at follow-up.

Diagnose

Classify the type of constipation — drives treatment choice

Type classified

Primary / Functional

No identifiable organic cause. Subdivide: Normal transit (most common — stool moves normally, perception altered), Slow transit (prolonged colonic transit — severe, infrequent), Defaecatory dysfunction (outlet obstruction, pelvic floor dyssynergia)

Secondary — Metabolic

Hypothyroidism (check TSH), hypercalcaemia (check Ca²⁺), hypokalaemia, diabetes, uraemia. Treat underlying cause first

Secondary — Neurological

Parkinson's disease, MS, spinal cord lesion, autonomic neuropathy. Often severe, refractory to standard laxatives

Secondary — Structural

Anal fissure (painful defaecation → avoidance), rectal prolapse, rectocele, colorectal cancer. PR exam essential

Drug-induced

Opioids (very common on regular opioids), iron, calcium channel blockers, TCAs. Review indication, dose and route; regular stimulant ± osmotic laxative; PAMORA only after appropriate laxative treatment (criteria differ: naloxegol TA345, naldemedine TA651)

Clozapine-associated GI hypomotility

Slow gut transit is common and can progress to impaction, ileus, obstruction, bowel ischaemia and death — manage proactively (Step 7)

Faecal impaction

Hard stool loading, sometimes with overflow — exclude obstruction and treat as impaction (Step 7)

IBS-C

Constipation + abdominal pain relieved by defaecation + Rome IV IBS criteria. Manage as IBS with specific pathway — do not label as functional constipation if IBS-C fits better

Classification directly changes treatment. Hypothyroidism-associated constipation resolves with levothyroxine — laxatives are a sticking-plaster. Opioid-induced constipation does not respond adequately to bulk-forming laxatives; it requires osmotic/stimulant laxatives or PAMORAs (naloxegol, methylnaltrexone). Defaecatory dysfunction responds to biofeedback pelvic floor physiotherapy, not laxatives. Getting this right at Step 3 avoids months of ineffective treatment.

Diagnose

Targeted examination — PR exam where it will change management

Examination completed and documented

Abdomen

Palpate all 4 quadrants. Faecal loading (doughy, indentable masses in LIF/RIF). Organomegaly. Tenderness. Visible distension or peristalsis

Perianal inspection

Haemorrhoids, fissures (look for sentinel tag), skin tags, prolapse, soiling. Do not proceed to PR if fissure causing severe pain without LA cream first

Digital rectal exam (PR)

With explanation and consent — for new, unexplained or refractory constipation, suspected impaction, obstructed defaecation, bleeding, anal symptoms, suspected mass or neurological disease (not every uncomplicated case). Assess resting tone, voluntary squeeze and simulated evacuation where relevant, but do not diagnose dyssynergic defaecation from PR examination alone — high resting tone may reflect pain, anxiety or guarding; confirmation needs specialist anorectal physiology (usually balloon expulsion and manometry). Faecal impaction (hard stool in rectum). Masses. Tenderness. A normal or empty rectum does not exclude proximal faecal loading or slow-transit constipation

Thyroid

Goitre → check TFTs if not recently done

Neurological screen

If saddle anaesthesia, urinary symptoms, or leg weakness → emergency assessment/MRI — do not delay referral for a primary-care neurological examination

BMI / nutrition

Low BMI + constipation → consider eating disorder, malnutrition, or cancer

PR examination is valuable when impaction or outlet dysfunction is suspected — a stimulant alone in faecal impaction can worsen pain. An anal fissure will be perpetuated if the underlying constipation is not treated. PR findings cannot diagnose dyssynergia — suspected defaecatory disorders need specialist anorectal physiology, not more laxatives. Missing a rectal mass on PR examination is an avoidable medicolegal failure.

Diagnose

Investigations — targeted, not routine; exclude secondary causes

Appropriate investigations ordered

Usually not routine

FBC, U&E, calcium, TFTs and CRP are not required for every patient with straightforward, recent constipation and no red flags. Abdominal X-ray is not a routine test for constipation or impaction. Calprotectin is not appropriate for isolated constipation

Bloods by context

FBC + ferritin/iron studies (bleeding, weight loss, systemic symptoms, older age, cancer concern) U&E / Ca²⁺ (frail, older, dehydrated, diuretics, CKD, recurrent impaction, suspected metabolic cause) TSH (symptoms suggest hypothyroidism, or no alternative explanation) Glucose / HbA1c (diabetes or autonomic neuropathy possible) CRP (only if IBD a realistic differential)

If suspected cancer pathway criteria met

Colorectal suspected cancer pathway referral + FBC U&E (renal function before CT contrast) LFTs while awaiting colonoscopy

Coeliac screen

Anti-tTG IgA + total IgA — particularly where IBS is suspected, symptoms are persistent, or there is iron deficiency

Stool calprotectin

Not for isolated constipation — only if IBD is a realistic differential (diarrhoea, blood, pain, weight loss, raised CRP); interpret with local pathway cut-offs

Imaging

Plain AXR: not a routine test for constipation or impaction; suspected obstruction needs urgent hospital assessment. CT abdomen/pelvis: urgent referral decision, not first-line in primary care

Do NOT routinely order

Colonoscopy without red flags / suspected cancer pathway criteria · Transit studies (specialist only) · Defaecating proctogram (specialist only) · Anorectal manometry (specialist only)

Secondary causes are uncommon but worth targeted testing. Hypercalcaemia is often asymptomatic but causes severe refractory constipation. Over-investigating functional constipation wastes NHS resource and delays treatment. Calprotectin helps only when IBD is a realistic alternative.

Refer

Referral criteria — know when primary care management is insufficient

Referral decision made

999 Emergency

Suspected bowel obstruction, perforation, volvulus, peritonitis, shock or severe uncontrolled pain → same-day (urgent) hospital assessment; call 999 if unstable or cannot be safely transported. Immediate emergency assessment for new urinary retention, saddle anaesthesia, bilateral leg weakness or rapidly progressive neurological deficit (suspected cauda equina syndrome)

Same-day

Faecal impaction with overflow needs same-day clinical review (not automatically hospital) if: significant pain or distension · vomiting or dehydration · suspected obstruction · frail or clinically unstable · rectal treatment needed but cannot be safely delivered in the community · no response to an appropriate disimpaction plan

Suspected cancer Colorectal

Per NICE NG12, offer FIT for: change in bowel habit or IDA at any age · rectal bleeding with abdominal pain or weight loss under 50 · unexplained weight loss and abdominal pain at 40+ · unexplained rectal bleeding, abdominal pain or weight loss at 50+ · abdominal mass · anaemia (even without iron deficiency) at 60+ → urgent referral if FIT ≥10 µg Hb/g · rectal mass, or unexplained anal mass or anal ulcer → consider a suspected cancer pathway referral without waiting for FIT · do not reassure solely on a negative or unreturned FIT if symptoms persist or concern remains · follow local colorectal pathways

Urgent gastroenterology

Suspected IBD (elevated calprotectin, bloody mucus, systemic symptoms) · Confirmed unexplained iron-deficiency anaemia with constipation → FIT and coeliac serology per local pathway, with upper and lower GI assessment in men and postmenopausal women even if FIT is negative

Routine gastroenterology / colorectal

Refractory constipation by clinical need (severe symptoms, recurrent impaction, suspected defaecatory dysfunction, neurological disease, weight loss, nutritional impact) — not a fixed 6-month wait · Suspected defaecatory dysfunction (for anorectal physiology) · Suspected slow-transit constipation for transit studies

Specialist nurse / Physio

Defaecatory dysfunction → pelvic floor biofeedback. Refer to continence nurse or specialist physiotherapist

Primary care manages

New functional constipation · Medication-induced constipation · Mild–moderate severity · Adequate response to laxatives

NICE NG12 suspected cancer pathway criteria have strong evidence — failure to refer appropriately is a leading cause of delayed colorectal cancer diagnosis in the UK. Symptoms alone do not establish dyssynergia — anorectal manometry and balloon expulsion are specialist tests; biofeedback is first-line specialist treatment once confirmed, and not useful without a defaecatory disorder. Identifying who needs specialist input early avoids prolonged ineffective treatment.

Treat

Treatment ladder — stepwise laxative therapy with patient-specific branching

Treatment initiated and documented

Always combine with lifestyle (Step 8). Choose first-line based on constipation type.

Functional constipation (first-line)

Bulk-forming or macrogol, by stool type 1st line

Choose by stool type: ispaghula if stools small/hard with adequate fluid; macrogol if hard stools, faecal loading or bulk poorly tolerated. Avoid bulk-forming agents in obstruction, impaction, severe slow transit or poor fluid intake. Titrate to a soft, formed stool

Opioid-induced constipation

Regular stimulant ± osmotic 1st line

Prescribe regular laxative treatment when initiating a strong opioid (NICE CG140). Choose a stimulant, osmotic agent or combination according to stool consistency, patient factors and local protocol. Continue for as long as the opioid-related risk persists, with review at each opioid review; review opioid indication, dose and route. Do NOT use bulk-forming agents alone

Faecal impaction (acute)

High-dose macrogol Acute

Exclude obstruction, severe pain, peritonism and significant vomiting first. Confirm the clinical diagnosis and exclude mechanical obstruction. Do not use oral disimpaction with suspected obstruction, peritonism or significant vomiting. High-dose macrogol: follow the specific product SPC, as reconstitution volumes and maximum licensed doses vary; review hydration, renal function, heart failure and aspiration risk; stop and reassess if colic, vomiting or distension increase. Consider rectal treatment where stool is low in the rectum or oral therapy is unsuitable. Reassess if no meaningful response within the expected timeframe. A stimulant is not adequate alone; adding one once obstruction is excluded is optional, not mandatory

Clozapine-associated GI hypomotility

Regular stimulant + osmotic/softener Proactive

Ask specifically about bowel frequency and stool consistency (often under-reported); keep a bowel chart, especially during initiation and dose changes; treat a change from baseline promptly. Avoid relying on bulk-forming laxatives alone (slow transit is common). Pain, distension, vomiting, overflow diarrhoea or systemic illness → same-day urgent medical assessment; do not wait several days to escalate (SPS)

The ladder below suits uncomplicated functional constipation; otherwise select by stool consistency, impaction risk, fluid intake, mobility, comorbidity and likely mechanism. Local formulary: ispaghula and macrogols are first-choice options, lactulose an alternative; naloxegol, naldemedine and prucalopride per their criteria.

Small, hard stools; adequate fluid; no impaction/obstruction

Ispaghula or another bulk-forming agent

Hard stools, faecal loading, poor response to or poor tolerance of bulk

Macrogol

Soft stool but difficult evacuation, or slow transit

Stimulant laxative, with or without osmotic treatment

Opioid-induced constipation

Regular stimulant laxative, usually with an osmotic agent as required

Suspected impaction

Treat as impaction after excluding obstruction

Pelvic-floor/outlet symptoms

Avoid simply escalating oral laxatives; assess and refer appropriately

Step 1Bulk-forming or osmotic first by stool consistency (above). Review in 2–4 weeks

Step 2Add osmotic laxative: Macrogol (Movicol) 1–3 sachets/day OR Lactulose 15ml BD (less preferred — causes bloating). Can combine with Step 1

Step 3Add stimulant laxative: Senna 7.5–15 mg nocte OR Bisacodyl 5–10mg nocte. Long-term use may be appropriate when clinically indicated (opioids, neurological disease, immobility, recurrent impaction, clozapine) — review regularly, titrate to effect and monitor for diarrhoea, dehydration and electrolyte disturbance; MHRA restrictions on over-the-counter stimulants concern short-term self-care, not prescribed use. Review need at each appointment. Can combine Steps 1+2+3

Step 4Opioid-induced: PAMORA — naloxegol (NICE TA345): inadequate response = at least moderate symptoms in ≥1 stool-symptom domain while taking ≥1 laxative class for ≥4 days in the previous 14. Naldemedine (NICE TA651): adults who have previously received laxative treatment (no 4-in-14-day definition). For both: exclude suspected or confirmed GI obstruction; review opioid indication, dose and route; check renal and hepatic function where relevant; check CYP3A interactions (particularly naloxegol); warn about abdominal pain, diarrhoea and possible opioid-withdrawal symptoms; analgesia may rarely be reduced — review promptly; follow the current SPC and local formulary. Methylnaltrexone mainly via specialist/palliative pathways

Step 5Specialist / experienced clinician only — not a routine step for all adults: Prucalopride (NICE TA211) — only for women with chronic constipation who have tried ≥2 laxatives from different classes at the highest tolerated recommended doses for ≥6 months without adequate relief, are being considered for invasive treatment, and are managed by a clinician experienced in chronic constipation. Usual dose 2 mg OD; in women over 65 start 1 mg OD and increase to 2 mg if needed and tolerated. Review after 4 weeks and reconsider if inadequate benefit; check the SPC for renal impairment and contraindications. Linaclotide (CG61) is for IBS with constipation, not uncomplicated functional constipation — confirm IBS-C diagnostic criteria; only after inadequate response to optimal or maximum tolerated laxatives from different classes and constipation for ≥12 months; review after 3 months; diarrhoea is common — stop or review if severe

RectalIf impaction / acute: Glycerol suppositories 4g PR · Sodium docusate enema · Phosphate enema (hospital/district nursing; avoid in significant renal impairment, heart failure, dehydration or electrolyte disturbance). Use alongside oral treatment, not instead

Key monitoring

U&E only where indicated: older/frail, CKD, heart failure, high-dose or prolonged use, diarrhoea/dehydration, diuretics · Review opioid dose — reduce if possible

Duration

Treat underlying cause. Functional constipation: minimum 4 weeks, reassess. Opioid-induced: treat for duration of opioid therapy

Next steps: see Constipation (adult) · Irritable bowel syndrome · Palliative constipation · Opioids in non-cancer pain

Bulk-forming agents work by increasing stool bulk and water content — they require adequate hydration to work. Macrogol is preferred over lactulose (Cochrane review: superior efficacy, less bloating). Stimulant laxatives are effective; long-term prescribed use is appropriate when clinically indicated, with regular review and monitoring for diarrhoea, dehydration and electrolyte disturbance. Prucalopride (5-HT₄ agonist): NICE TA211 restricts use to women failing ≥2 laxative classes over ≥6 months under experienced supervision. Naloxegol (PAMORA) peripherally blocks opioid receptor in gut without reversing analgesia — KODIAC trials showed significant improvement in opioid-induced constipation vs placebo.

Lifestyle

Non-pharmacological interventions — essential alongside all laxatives

Lifestyle advice given and documented

Lifestyle is treatment, not afterthought. Practical measures worth addressing alongside laxatives.

Dietary fibre Gradual, individualised adjustment of soluble fibre where appropriate — no universal daily target. Avoid increasing fibre substantially in suspected obstruction, faecal impaction, severe slow-transit constipation, significant bloating, some patients with pelvic-floor dysfunction, or clozapine-associated hypomotility unless advised and adequately hydrated

Fluid intake Adequate fluid where not contraindicated — no fixed volume for everyone; individualise for heart failure, CKD, hyponatraemia, cirrhosis, frailty or fluid restriction. Reduce caffeine and alcohol which worsen dehydration

Physical activity Regular activity as able — a practical supportive measure

Toilet habit — defaecation timing Use the gastrocolic reflex: an unhurried toilet routine after a meal, often breakfast. Never ignore the urge. Allow adequate time — do not rush

Toilet posture A footstool to raise the feet is a reasonable low-risk measure that may make evacuation easier — no specific height is evidence-based or essential

Medication review Stop or switch constipating medications where clinically safe. Discuss opioid dose reduction or rotation with pain team if appropriate

Stress and anxiety Address anxiety or distress where present (NHS Talking Therapies) — not a routine constipation treatment

Bowel diary Ask patient to complete 1-week bowel diary (BSC type, frequency, straining, pain). Invaluable for monitoring response and specialist referral

Soluble fibre can improve stool frequency, but fibre and fluid advice must be individualised. Activity, responding to the urge, privacy, time and a footstool are low-cost practical measures.

Safety

Follow-up & monitoring — safety-net, reassess, and step down

Follow-up plan documented and safety-net given

2–4 weeks

First review (sooner for impaction, clozapine or frailty): stool form, frequency, straining, pain, bloating, episodes of overflow and adverse effects (bloating, colic); review medication causes and opioid requirement; electrolytes/renal function where clinically indicated. Adjust laxative dose or add next step if insufficient response

6–8 weeks

Reassess symptom severity. Check bloods if ordered. If no improvement despite Step 3 → consider referral and specialist investigation. Refer if persistent severe symptoms, recurrent impaction, suspected pelvic-floor dysfunction, neurological disease, nutritional impact or failure of appropriate treatment

3 months

Full review: is laxative still needed? Attempt step-down in mild resolved cases — long-term laxatives are appropriate and safe for many (opioids, neurological disease, immobility, recurrent impaction). Reassess dietary adherence, medication causes

Ongoing (opioid-induced)

Laxative treatment should continue for the duration of opioid therapy — review at every opioid prescription review

Urgent / 999 Safety-net

Same-day (urgent) hospital assessment for suspected obstruction (vomiting, severe distension, no flatus) or signs of perforation (severe pain, rigid abdomen, fever) — call 999 if collapsed, unstable or unable to travel safely. New urinary retention, saddle numbness or leg weakness → immediate emergency assessment

Same-day GP Safety-net

Any new rectal bleeding · Significant weight loss · Anal/rectal mass found · Worsening pain · Faecal impaction not resolving after 3 days of treatment

Return to Step 1

If new red flags emerge at ANY point — immediately re-screen. Constipation can mask new colorectal malignancy even in previously established "functional" patients

Relapse is common if contributing factors persist. Monitor electrolytes selectively in higher-risk patients. A patient with "established" functional constipation who develops new rectal bleeding needs re-screening — interval colorectal cancers do occur. Structured safety-netting is an RCGP SCA competency marker — document what you told the patient to watch for.