How do I diagnose and manage irritable bowel syndrome (IBS) according to Rome IV criteria?

Diagnosis and Management of Irritable Bowel Syndrome Using Rome IV Criteria

Diagnose IBS using Rome IV criteria when a patient has recurrent abdominal pain at least 1 day per week in the last 3 months (with symptom onset at least 6 months prior) associated with two or more of: pain related to defecation, change in stool frequency, or change in stool form—but only after excluding organic disease through targeted investigation based on age and alarm features. 1, 2

Diagnostic Algorithm

Step 1: Apply Rome IV Diagnostic Criteria

The Rome IV criteria require all of the following 1, 2:

• Recurrent abdominal pain at least 1 day per week in the last 3 months
• Symptom onset at least 6 months before diagnosis
• Two or more of these associations:
  • Pain related to defecation
  • Associated with change in stool frequency
  • Associated with change in stool form/appearance

Critical caveat: Abdominal pain is mandatory—without pain, IBS cannot be diagnosed. 3 Rome IV is substantially more restrictive than Rome III, reducing global IBS prevalence from 10.1% to 4.1%, and identifies patients with more severe symptoms and higher psychological comorbidity. 1

Step 2: Assess for Alarm Features ("Red Flags")

Mandatory investigations are required if any of the following are present 2, 4:

• Unintentional weight loss
• Rectal bleeding or hematochezia
• Nocturnal symptoms (diarrhea or pain waking patient from sleep)
• Anemia
• Fever
• Family history of colorectal cancer or inflammatory bowel disease
• Age >50 years (requires colonoscopy due to colorectal cancer risk) 4
• Right lower quadrant pain (requires urgent evaluation for appendicitis, IBD, or cecal pathology) 2

Key distinguishing feature: Absence of nocturnal symptoms helps separate IBS from organic gastrointestinal disease. 2

Step 3: Perform Targeted Investigations Based on Clinical Context

For patients WITHOUT alarm features:

• Age <45 years, female, symptom duration >2 years, frequent past visits for non-GI symptoms: A working diagnosis can be made safely in general practice based on typical symptoms, normal physical examination, and absence of alarm features. 4, 5

For patients WITH atypical symptoms, short history, or age >45 years 5, 4:

• Sigmoidoscopy or colonoscopy
• Complete blood count (to exclude anemia)
• Thyroid function tests (especially for constipation-predominant symptoms) 2
• Antiendomysial antibodies (to exclude celiac disease) 2
• Stool microscopy

For diarrhea-predominant IBS (IBS-D) 2:

• Sigmoidoscopy with biopsies to detect microscopic colitis
• Consider bile-acid diarrhea: SeHCAT testing or empirical trial of bile-acid sequestrant (highest response when SeHCAT retention <10%) 2

For constipation-predominant IBS (IBS-C) 2:

• Evaluate for hypothyroidism
• Test for celiac disease

Step 4: Subtype IBS Based on Predominant Stool Pattern

Once IBS is diagnosed, classify by predominant bowel habit 5:

• IBS-D (diarrhea): Loose/watery stools predominate
• IBS-C (constipation): Hard/lumpy stools predominate, <3 bowel movements per week 4
• IBS-M (mixed): Alternating patterns

Important note: IBS-M is the least stable subtype, with 31.7% of patients changing subtypes within 12 months under Rome IV criteria. 6

Management Algorithm

Step 1: First-Line Therapy (4 weeks)

For IBS-C 5, 2:

• Water-soluble dietary fiber (25 g/day)
• Osmotic laxatives
• Linaclotide or lubiprostone

For IBS-D 5:

• Loperamide
• Ondansetron
• Ramosetron
• Eluxadoline

For IBS-M 5:

• SSRIs
• Rifaximin
• Antispasmodics
• Psychological therapy

Concurrent interventions for all subtypes 2:

• Identify and address food intolerances
• Ensure adequate time for regular defecation
• Encourage appropriate exercise

Step 2: Second-Line Therapy for Non-Responders (4 weeks)

Combination of different mechanistic gut-targeted agents and/or psychopharmacological agents with basic psychotherapy. 7

Step 3: Third-Line Therapy for Persistent Non-Responders

Combination of gut-targeted pharmacotherapy, psychopharmacological treatments, and specific psychotherapy. 7

Critical Clinical Pearls

Communicate the diagnosis confidently: Use simple explanations of gut-brain interaction and visceral hypersensitivity. Explain that IBS is a chronic, fluctuating disorder triggered by stress, illness, medications, and dietary factors, but is not associated with increased risk of cancer or mortality. 2

Prognosis factors 5:

• Patients with longer symptom history are less likely to improve
• Chronic ongoing life stress virtually precludes recovery (0% recovery vs. 41% without such stresses in 16-month follow-up)

Once functional diagnosis is established: The incidence of new non-functional diagnoses is extremely low, so avoid repeated unnecessary investigations. 4

Post-infectious IBS (PI-IBS): If symptoms developed immediately following acute gastroenteritis (with positive stool culture or ≥2 of: fever, vomiting, diarrhea), and patient did not meet IBS criteria prior to acute illness, diagnose as PI-IBS. Most PI-IBS cases are IBS-M or IBS-D subtypes. 5