Irritable Bowel Syndrome
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Direct answer
Recurrent abdominal pain, present at least one day per week for the last three months with onset at least six months earlier, that relates to defaecation and associates with a change in stool frequency or form — those are the Rome IV criteria, and unlike Rome III they demand pain, not mere discomfort. Diagnosis is positive and symptom-based, supported by limited targeted testing: full blood count, CRP, coeliac serology and faecal calprotectin (to exclude inflammatory bowel disease, with a low calprotectin genuinely reassuring), with stool microscopy in Indian practice where giardiasis and other enteric infection masquerade as IBS. Therapy follows the subtype — antispasmodics and low-FODMAP diet for pain, loperamide or rifaximin 550 mg three times daily for two weeks for IBS with diarrhoea, soluble fibre then secretagogues such as lubiprostone or linaclotide for IBS with constipation — with low-dose amitriptyline as the neuromodulator of choice for refractory pain.
What you must remember
- Rome IV verbatim essentials: pain at least one day/week for three months, onset six months prior, related to defaecation, plus changed frequency or Bristol form; the word "discomfort" was deliberately deleted from Rome III.
- Subtypes by Bristol stool chart: IBS-C over a quarter of stools type 1-2, IBS-D over a quarter type 6-7, IBS-M mixed, IBS-U unclassified — the subtype decides the drug, so classify before prescribing.
- Faecal calprotectin: a value under about 40-50 µg/g reliably separates IBS from IBD and reduces colonoscopies; a raised value demands endoscopy, and steroids thrown at a raised calprotectin without biopsy is how Crohn's gets missed.
- Red flags that break the IBS label: onset after age 50, nocturnal symptoms rousing sleep, rectal bleeding, weight loss, family history of colorectal cancer, iron-deficiency anaemia, and a palpable mass or lymphadenopathy.
- IBS-D shelf: loperamide for stool frequency, rifaximin 550 mg thrice daily for 14 days (non-absorbed antibiotic, repeat courses possible), eluxadoline 100 mg twice daily (mu-opioid agonist, contraindicated if prior cholecystectomy or pancreatitis), cholestyramine for bile-salt diarrhoea.
- IBS-C shelf: ispaghula or other soluble fibre first, polyethylene glycol for stool, then lubiprostone (chloride channel activator) or linaclotide (guanylate cyclase-C agonist) — both prescription secretagogues with mechanistic exam appeal.
- Neuromodulation: tricyclics such as amitriptyline 10-25 mg at night help IBS-D pain and sleep; SSRIs suit IBS-C with anxiety; response is at analgesic-antidepressant dosing far below psychiatric doses.
- Post-infectious IBS: risk rises about seven-fold after bacterial gastroenteritis — an Indian exam favourite given the ubiquity of enteric infections; the mechanism is low-grade mucosal inflammation and enteroendocrine cell hyperplasia.
A 15-minute clinic consultation
A 24-year-old student reports three years of lower abdominal cramping relieved by passing stool, alternating with loose and pellet stools, worse before examinations, with no weight loss, no bleeding, no nocturnal diarrhoea. She fulfils Rome IV on history alone; the consultation adds haemoglobin, CRP, tTG-IgA, faecal calprotectin and stool microscopy for parasites — all normal — and no colonoscopy is indicated at her age with negative tests. Management is explained as a real disorder of gut-brain interaction, not imagination: regular meals, limited caffeine, a two-to-four week trial of a dietitian-supervised low-FODMAP diet with staged reintroduction, mebeverine or peppermint oil for spasms, and ispaghula for constipation days. Six weeks later pain persists on the diarrhoea-dominant pattern, so rifaximin 550 mg thrice daily for two weeks is prescribed, and amitriptyline 10 mg at night is reserved as the next step if pain continues to drive absenteeism.
The same appointment documents what would change the label — a rising calprotectin, new anaemia, nocturnal waking — converting a symptom diagnosis into a diagnostic pathway if betrayed later.
How NEET-PG frames it
The stem almost always hides the diagnosis inside the pain-stool relationship: pain relieved by defaecation with altered form equals IBS, while pain with a raised calprotectin or nocturnal diarrhoea equals IBD until excluded — the single most examined discrimination. Drug-matching questions are common: loperamide to IBS-D, linaclotide to IBS-C, rifaximin to IBS-D without constipation, amitriptyline to pain-predominant IBS-D — a wrong subtype gives a wrong answer even when the drug is real. Indian papers also test mimics: giardiasis producing bloating and loose stools (stool microscopy before committing to IBS), lactose intolerance producing pure diarrhoea without pain, and microscopic colitis producing watery diarrhoea in an older patient on NSAIDs — the last is a colonoscopy-with-biopsy diagnosis, never an IBS diagnosis.
Frequently asked questions
What are the Rome IV criteria for IBS?
Recurrent abdominal pain at least one day per week for three months (onset six months earlier) related to defaecation and associated with a change in stool frequency or form — pain is now mandatory, unlike Rome III's "discomfort".
Which single stool test best separates IBS from IBD?
Faecal calprotectin — a value under roughly 40-50 µg/g argues strongly against mucosal inflammation, whereas a raised value mandates colonoscopy with biopsies.
Which antibiotic is used for IBS with diarrhoea?
Rifaximin 550 mg three times daily for 14 days — a non-absorbed antibiotic that improves global symptoms and bloating in IBS-D, with repeat courses considered for recurrence.
What is first-line for IBS with constipation?
Soluble fibre such as ispaghula plus polyethylene glycol for stool output, escalating to intestinal secretagogues such as lubiprostone or linaclotide if insufficient; lubiprostone and linaclotide are also safe in pregnancy-relevant counselling contexts where older agents fail.
When should IBS be diagnosed without colonoscopy?
In patients under about 45-50 with typical Rome IV symptoms, normal basic bloods, coeliac serology, calprotectin and stool microscopy, and no red flags — colonoscopy is reserved for atypical or older patients or those with positive screening tests.