Gastrointestinal Gastroenterology · Clinical

ROME IV — IBS Criteria

The ROME IV criteria (2016) define irritable bowel syndrome by symptom-based diagnostic standards — allowing confident diagnosis without invasive investigation in the absence of alarm features.

✦ The Mnemonic

"Recurrent Pain, Once Weekly, Linked to Stool"

Recurrent abdominal pain · ≥1 day/week · associated with defecation or stool change

R Recurrent abdominal pain The cardinal symptom — must be recurrent, not a single episode
W ≥1 day per week On average at least one day per week in the last 3 months
O Onset ≥6 months ago Symptom onset at least 6 months before diagnosis
L Linked to defecation Pain associated with defecation — better or worse after opening bowels
S Stool frequency change Associated with change in frequency of stool
F Form (consistency) change Associated with change in form/appearance of stool — Bristol Stool Scale

📚 Clinical Breakdown

ROME IV requires recurrent abdominal pain averaging ≥1 day per week for the last 3 months, with symptom onset at least 6 months prior, AND at least 2 of the 3 stool-related criteria (linked to defecation, change in frequency, change in form). The previous ROME III threshold was ≥3 days per month — ROME IV raised this to better identify true IBS.

IBS subtypes are classified by predominant stool pattern: IBS-C (constipation predominant — >25% hard stools), IBS-D (diarrhoea predominant — >25% loose stools), IBS-M (mixed), and IBS-U (unclassified). Subtyping guides treatment — antispasmodics and laxatives for IBS-C; loperamide and low-FODMAP diet for IBS-D.

Alarm features that mandate investigation before diagnosing IBS: age >50 at first presentation, rectal bleeding, unexplained weight loss, nocturnal symptoms waking the patient, family history of colorectal cancer or IBD, iron-deficiency anaemia, raised CRP/faecal calprotectin. Positive alarm features should prompt colonoscopy.

Minimum frequency ≥1 day/week average over last 3 months
Minimum duration Symptoms onset ≥6 months ago
Stool criteria needed ≥2 of 3 (defecation link, frequency change, form change)
Alarm feature investigation Colonoscopy ± bloods if any alarm feature present

⭐ Clinical Pearl

Faecal calprotectin is the key test to distinguish IBS from inflammatory bowel disease (IBD). A level <50 µg/g has a very high negative predictive value for IBD — making colonoscopy unnecessary in low-risk patients with typical IBS symptoms and no alarm features. It is now recommended as a first-line test before endoscopy in suspected IBS.

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