Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Make a confident positive diagnosis of irritable bowel syndrome after proportionate exclusion of important disease, then deliver phenotype-led dietary, pharmacological and behavioural care with explicit safety-netting.
IBS is a chronic, relapsing disorder in which altered motility, visceral sensitivity, mucosal signalling, microbiota, diet and central processing can contribute in different proportions. The diagnosis is clinically meaningful: abdominal pain is associated with defaecation or a change in stool frequency or form, accompanied by symptoms such as urgency, incomplete evacuation, mucus and bloating. Establish duration, Bristol stool form, pain-stool relationship, nocturnal symptoms and impact. Ask sensitively about faecal incontinence, pelvic-floor symptoms, eating restriction, anxiety and previous gastroenteritis. IBS-D, IBS-C and IBS-M are management phenotypes rather than fixed identities. Symptoms may overlap functional dyspepsia, reflux, migraine, fibromyalgia and pelvic pain without making any of them unreal.
Proportionate investigation protects against both missed organic disease and harmful overtesting. Review family history, bleeding, anaemia, weight trajectory, fever, nocturnal diarrhoea, older-age onset, masses, recent antibiotics, travel, medicines and gynaecological features. A typical stable adult generally needs full blood count, CRP or ESR and coeliac antibodies. Faecal calprotectin helps distinguish inflammatory bowel disease from a functional disorder when cancer is not suspected and the local pathway regards it as appropriate. FIT, endoscopy or imaging responds to cancer criteria or specific discordant findings, not patient anxiety alone. Normal routine tests
Genetic, developmental and psychosocial factors shape visceral sensation and central pain regulation, creating vulnerability without a single diagnostic lesion.
Some IBS begins after gastroenteritis, with persistent immune, barrier and microbiome changes despite clearance of the original pathogen.
Fermentable carbohydrates, irregular meals, sleep disruption and stress can amplify symptoms, but response to a trigger does not establish an allergy or intolerance.
Ordinary gas, stool or bowel contraction generates exaggerated afferent signalling and pain because peripheral and central thresholds are altered.
Variable transit and fluid handling produce constipation, diarrhoea or a mixed pattern that can shift over time.
Pain, autonomic arousal, attention and avoidance feed back on motility and sensation, sustaining genuine symptoms without structural inflammation.
Recurrent abdominal pain associated with loose stools, urgency or defaecation, with a stable examination and no inflammatory, malignant or malabsorptive signal, supports IBS-D after proportionate testing.
Pain, bloating, hard or infrequent stools and incomplete evacuation fit IBS-C. Marked straining, digital manoeuvres or a sense of blockage should also raise a defaecatory pelvic-floor disorder.
A palpable mass, iron-deficiency anaemia, rectal bleeding or an age- and symptom-qualified bowel change must be assessed using current NG12 and FIT pathways rather than explained by longstanding IBS.
Post-cholecystectomy watery urgency, ileal disease or exposure to metformin, magnesium, laxatives or other diarrhoeal medicines can produce a treatable phenotype that should not be relabelled automatically.
Bleeding, nocturnal symptoms, weight loss, objective inflammation or raised calprotectin favours IBD over a typical IBS phenotype.
Positive serology obtained while eating gluten and compatible enteropathy identify coeliac disease, which may otherwise mimic IBS with diarrhoea or bloating.
Older-onset change, anaemia, mass or bleeding requires cancer assessment; nocturnal watery stool or post-ileal diarrhoea directs colonic biopsies or bile-acid testing.
Blood mixed with stool, night-time diarrhoea, fever, raised inflammatory markers, perianal disease or progressive weight loss is discordant and requires assessment for IBD, infection or microscopic colitis.
Iron or folate deficiency, weight loss, mouth ulcers, dermatitis herpetiformis, autoimmune disease or a family history supports coeliac testing while the patient continues eating gluten.
Unsupervised exclusion diets can reduce fibre, calcium and overall diversity, worsen constipation and create anxiety around food.
Repeated low-yield testing or escalating laxative, antidiarrhoeal and analgesic use can cause adverse effects and undermine a confident diagnosis.
Pain, urgency and unpredictable stool disrupt work, travel, intimacy and mental health despite IBS not causing inflammation, bleeding or cancer.
A symptom pattern plus targeted normal tests can positively identify IBS. Explaining the evidence and mechanism often reduces more anxiety than saying that every investigation is normal.
An individual can move from IBS-C to IBS-M or IBS-D as disease, diet and medicines change. Reclassify the current phenotype before simply repeating an old prescription.
Insoluble bran increases stool bulk and fermentation and may intensify pain, whereas slowly introduced soluble fibre can improve global symptoms. Asking only whether fibre was tried hides this distinction.
It helps separate inflammatory bowel disease from functional symptoms in a defined population. It is not a generic bowel-cancer test and may be normal in microscopic colitis.
The purpose of low-FODMAP restriction is to identify tolerable triggers, not maintain maximal exclusion. Reintroduction widens nutrition, cost and social choice while preserving symptom benefit.
Diagnosing IBS from bloating alone without the defining abdominal-pain and bowel-habit relationship.
Repeating colonoscopy for a stable typical phenotype while omitting coeliac serology.
Using faecal calprotectin as a colorectal cancer rule-out test or as proof of microscopic colitis.
Advising more bran to every constipated patient despite worsening pain and distension.
Allowing an unsupervised exclusion diet to become nutritionally inadequate and socially disabling.
Attributing new rectal bleeding or iron deficiency to a historic IBS diagnosis.
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A 29-year-old has recurrent abdominal pain related to defaecation and alternating stool form for one year, with stable weight, normal examination and no warning features. Which initial investigation set best supports a positive IBS diagnosis?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
Management is collaborative experimentation with measurable goals. Explain the mechanism, agree which symptom matters most and change one or two variables at a time. Regular eating, adequate non-caffeinated fluid, exercise and adjustment of soluble fibre can be more sustainable than a dramatic diet. Medicines target stool form or pain and need review for benefit and adverse effects. Dietitian-led low-FODMAP treatment includes restriction, systematic reintroduction and personalisation to limit nutritional and social harm. Refractory symptoms call for a diagnostic reset and gut-directed CBT, hypnotherapy or another accessible psychological treatment where indicated. Follow-up should record function, not just pain, and reopen investigation when warning features emerge.
Avoid during acute bloody diarrhoea, fever, suspected ileus or severe inflammatory colitis. Excess dosing can cause constipation and serious cardiac toxicity; review continued need and response.
Escalation may increase gas or pain; avoid bulk agents in suspected obstruction. NICE discourages lactulose in IBS because it can worsen bloating, and persistent outlet symptoms need pelvic-floor assessment.
Discuss unlicensed symptom use where applicable, drowsiness, constipation, dry mouth, urinary retention, glaucoma, cardiac conduction, falls and overdose risk. Review at four weeks and avoid abrupt unsupervised changes.
Diarrhoea can be important; exclude mechanical obstruction and review hydration. NICE eligibility includes at least twelve months of constipation and failure of maximum tolerated prior laxatives.