What are the diagnostic steps for Irritable Bowel Syndrome (IBS)?

Diagnostic Steps for Irritable Bowel Syndrome (IBS)

IBS should be diagnosed based on positive symptom criteria using the Rome criteria, rather than as a diagnosis of exclusion, with limited investigations to rule out organic disease only when alarm features are present. 1

Symptom-Based Diagnostic Criteria

The diagnosis of IBS relies primarily on identifying characteristic symptoms:

Rome Criteria

• Rome III/IV Criteria: Recurrent abdominal pain or discomfort at least 1 day per week in the last 3 months, with symptoms present for at least 6 months, associated with at least 2 of the following:
  • Pain is relieved by defecation
  • Onset associated with change in stool frequency
  • Onset associated with change in stool form/consistency 1, 2

Supporting Symptoms

• Abnormal stool frequency (>3 BMs/day or <3 BMs/week)
• Abnormal stool form (lumpy/hard or loose/watery)
• Abnormal stool passage (straining, urgency, incomplete evacuation)
• Passage of mucus
• Bloating or abdominal distention 2

IBS Classification by Predominant Stool Pattern

• IBS-C: Hard stools >25% of the time and loose stools <25% of the time
• IBS-D: Loose stools >25% of the time and hard stools <25% of the time
• IBS-M: Mixed stool pattern (both hard and loose stools >25% of the time)
• IBS-U: Unclassified 1

Diagnostic Algorithm

1. Initial Assessment:

   • Complete history focusing on Rome criteria symptoms
   • Physical examination including abdominal and rectal examination
   • Screen for alarm features/red flags

2. Red Flags requiring further investigation:

   • Age >50 years at symptom onset
   • Short history of symptoms (<6 months)
   • Documented weight loss
   • Nocturnal symptoms
   • Family history of colorectal cancer or IBD
   • Anemia
   • Rectal bleeding
   • Recent antibiotic use 1, 2

3. Basic Laboratory Testing:

   • Complete blood count
   • Stool Hemoccult test
   • Consider ESR/CRP (especially in younger patients)
   • Consider serum chemistries and albumin 2

4. Subtype-Specific Testing:

   • For IBS-D:

     • Consider stool for ova and parasites in endemic areas
     • Consider celiac disease screening
     • Consider lactose/dextrose H2 breath test if lactose intolerance suspected
     • Consider colonoscopy with biopsies to rule out microscopic colitis in patients with risk factors (female sex, age ≥50 years, autoimmune disease, severe watery diarrhea, recent onset, weight loss, or use of NSAIDs/PPIs/SSRIs/statins) 2

   • For IBS-C:

     • Consider therapeutic trial of fiber first
     • For persistent symptoms, consider transit studies or defecography 2

   • For IBS with pain predominance:

     • Consider plain abdominal radiography during acute episodes 2

5. Age-Based Approach:

   • Patients ≤50 years with typical symptoms and no alarm features:

     • Limited or no additional testing
     • Confident positive diagnosis based on Rome criteria

   • Patients >50 years:

     • Colonoscopy recommended (due to higher risk of colorectal cancer) 2

Communicating the Diagnosis

After establishing the diagnosis:

• Clearly explain IBS as a disorder of gut-brain interaction
• Emphasize that IBS is not associated with increased mortality or cancer risk
• Explain that visceral hypersensitivity is a key pathophysiological aspect
• Discuss that symptoms may be triggered by stress, illness, medications, and eating
• Acknowledge that while cure is unlikely, substantial symptom improvement is achievable 2

Common Pitfalls to Avoid

• Overinvestigation: Once a functional diagnosis is established, avoid repetitive testing as the incidence of new non-functional diagnoses is extremely low 1
• Treating IBS-C with only laxatives: This fails to address the pain component 1
• Viewing IBS as a diagnosis of exclusion: This leads to unnecessary testing and healthcare costs 3
• Ignoring psychosocial factors: Psychological stress and psychosocial factors can significantly affect symptoms and treatment outcomes 2

By following this structured diagnostic approach, clinicians can confidently diagnose IBS, minimize unnecessary testing, and focus on effective symptom management strategies tailored to the patient's predominant symptoms.