NICE vs SIGN: Management of Irritable Bowel Syndrome (2025)

This guide provides a comparative overview of the National Institute for Health and Care Excellence (NICE) and the Scottish Intercollegiate Guidelines Network (SIGN) guidelines for the management of Irritable Bowel Syndrome (IBS) in adults. While both guidelines aim to standardise and improve care, there are notable differences in their approaches, reflecting evolving evidence and distinct methodological frameworks. This comparison is intended for UK clinicians to support informed, guideline-concordant practice.

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Diagnosis and Assessment

NICE (NG231, Published 2023)

NICE advocates for a positive diagnosis using the Rome IV criteria, emphasising that IBS should be considered if a person has had abdominal pain or discomfort for at least 6 months, associated with two or more of: relief by defecation, associated change in stool frequency, or associated change in stool form. Crucially, NICE recommends a limited, targeted approach to ruling out alternative diagnoses.

• Key Investigations: Full blood count (FBC), C-reactive protein (CRP), and coeliac serology. Endoscopy is not routinely recommended unless 'red flag' symptoms are present.
• Focus: A positive diagnosis based on symptom criteria to avoid over-investigation, reducing patient anxiety and healthcare costs.

SIGN (SIGN 157, Published 2024)

SIGN also supports a positive clinical diagnosis but provides a more detailed framework for assessment. It incorporates the Rome IV criteria but places a stronger emphasis on the clinical history and exclusion of alarm features.

• Key Investigations: Aligns with NICE on FBC, CRP, and coeliac serology. SIGN additionally suggests considering calprotectin testing to help distinguish from inflammatory bowel disease (IBD) in patients with diarrhoea-predominant symptoms, especially if there is diagnostic uncertainty.
• Focus: A comprehensive clinical assessment that includes a detailed dietary and psychosocial history from the outset.

Key Difference: SIGN provides more explicit guidance on the use of faecal calprotectin in the initial diagnostic work-up for IBS-D, whereas NICE considers it more in the context of reassuring patients with ongoing concerns.

Treatment Recommendations

First-Line Management: Diet and Lifestyle

Both guidelines agree on initial advice regarding regular meals, fluid intake, and exercise. The primary divergence is in dietary intervention.

• NICE: Recommends offering a low FODMAP diet as a second-line dietary therapy. First-line advice should include general dietary guidance (e.g., limiting fibre, caffeine, alcohol) and trial of probiotics.
• SIGN: Suggests a more structured first-line approach, including traditional advice and, if insufficient, a trial of a fermentable carbohydrate restriction diet (which includes but is not limited to the low FODMAP diet), ideally delivered by a trained dietitian.

Pharmacological Therapy

Both guidelines recommend a personalised, symptom-targeted approach.

• NICE: Provides a detailed, sequential pharmacological algorithm. Key recommendations include:
  • For abdominal pain: Antispasmodics (e.g., hyoscine butylbromide, mebeverine).
  • For constipation (IBS-C): Linaclotide or tenapanor.
  • For diarrhoea (IBS-D): A 2nd-line option of a low-dose tricyclic antidepressant (TCA) like amitriptyline (10-20 mg).
• SIGN: Offers similar recommendations but presents them as a menu of options rather than a strict sequence. SIGN gives equal weight to TCAs and SSRIs for patients with comorbid anxiety/depression or refractory pain, reflecting a slightly stronger emphasis on the gut-brain axis.

Psychological Therapies

Both acknowledge the role of psychological therapies for refractory symptoms.

• NICE: Recommends considering referral for psychological interventions (e.g., CBT, hypnotherapy) if symptoms do not respond to pharmacotherapy after 12 months.
• SIGN: Suggests a lower threshold for referral, recommending psychological therapies be considered for patients with significant symptom-related distress or poor quality of life, irrespective of a strict 12-month timeline.

Key Difference: The timing and threshold for psychological referral are lower in SIGN, and its dietary guidance is more integrated and explicitly dietitian-led from an earlier stage.

Special Situations

Refractory IBS

NICE provides a clear definition of refractory IBS (no response to all recommended therapies over 12 months) and suggests referral to a specialist team. SIGN focuses on a holistic review, re-evaluating the diagnosis, and ensuring all behavioural and psychological options have been adequately explored.

Post-Infectious IBS

SIGN offers specific advice, noting that post-infectious IBS is a recognised subtype (typically IBS-D) and may have a better prognosis. NICE does not differentiate management for this group specifically.

Practical Clinical Flow: A Synthesis

A pragmatic approach for UK clinicians, synthesising both guidelines, could be:

1. Assessment: Use Rome IV criteria. Check FBC, CRP, coeliac serology. Consider calprotectin for IBS-D, especially if diagnostic uncertainty exists.
2. First-Line: Provide education, reassurance, and lifestyle advice. Offer a trial of probiotics and/or antispasmodics based on dominant symptoms.
3. Second-Line (Diet): Refer to a dietitian for expert dietary advice, which may include a trial of a low FODMAP or fermentable carbohydrate restriction diet.
4. Second-Line (Pharmacological): Introduce symptom-targeted drugs (linaclotide for IBS-C, loperamide for IBS-D, TCAs for pain/diarrhoea).
5. Third-Line (Psychological): For ongoing distress or refractory symptoms, refer for CBT, gut-directed hypnotherapy, or other psychological therapies without undue delay.
6. Specialist Referral: For diagnostic uncertainty, refractory symptoms, or severe psychiatric comorbidity.

Frequently Asked Questions (FAQs)

1. Which guideline should I follow in Scotland or England?

Clinicians in Scotland are expected to follow SIGN guidance, while those in England and Wales follow NICE. However, the guidelines are largely complementary. The synthesis presented above provides a practical, evidence-based approach applicable across the UK.

2. How important is the low FODMAP diet?

Both guidelines recognise it as an effective strategy, but emphasise it should be supervised by a trained dietitian to ensure nutritional adequacy and proper reintroduction. SIGN integrates it slightly earlier and more explicitly into management pathways.

3. What is the first-choice drug for abdominal pain?

Both guidelines recommend antispasmodics (e.g., mebeverine) as first-line. For persistent pain, especially in IBS-D, low-dose amitriptyline (10-20 mg) is a strong second-line recommendation from both NICE and SIGN.

4. How do I manage a patient with significant anxiety?

SIGN places a stronger emphasis on the gut-brain axis. For patients with comorbid anxiety, consider TCAs or SSRIs earlier in the treatment pathway, alongside psychological therapies, as per SIGN's recommendations.

5. When should I refer for psychological therapy?

Do not wait 12 months if symptoms are causing significant distress. While NICE mentions 12 months of refractory pharmacotherapy, SIGN's lower threshold for referral is more patient-centred. Refer based on impact on quality of life.

Source Links

• NICE Guideline NG231 (2023): Irritable bowel syndrome in adults: diagnosis and management
  NICE NG231
• SIGN Guideline 157 (2024): Management of Irritable Bowel Syndrome
  SIGN guideline: irritable bowel syndrome

Disclaimer: This document is a comparative summary for educational purposes. Clinicians should refer to the full text of the guidelines for complete recommendations and context.