How should I evaluate and manage an adult with suspected irritable bowel syndrome without alarm features?

Evaluation and Management of Suspected Irritable Bowel Syndrome Without Alarm Features

Make a positive clinical diagnosis of IBS based on symptoms using the Rome criteria, perform limited baseline blood and stool tests to exclude organic disease, then initiate symptom-directed therapy without extensive investigation. 1

Diagnostic Approach

Step 1: Apply Clinical Diagnostic Criteria

Use the NICE definition for primary care: abdominal pain or discomfort associated with altered bowel habit for at least 6 months, in the absence of alarm symptoms. 1 This is more pragmatic than Rome IV criteria, which were derived from secondary care populations and may be overly restrictive. 1

The Rome criteria require at least 12 weeks of abdominal pain in the past 12 months with at least two of three features: 2

• Pain relieved by defecation
• Pain onset associated with change in stool frequency
• Pain onset associated with change in stool consistency

Key clinical features that increase IBS likelihood: 2

• Female sex (2:1 female predominance)
• Age under 45 years
• Symptom duration greater than 2 years
• Associated non-GI symptoms: lethargy, poor sleep, fibromyalgia (20-50% coexistence), backache, urinary frequency, dyspareunia

Step 2: Screen for Alarm Features

Any of the following mandates extended investigation and typically referral: 1, 3

• Age ≥45 years at symptom onset
• Unintentional weight loss
• Rectal bleeding (beyond minor hemorrhoidal)
• Anemia on complete blood count
• Nocturnal diarrhea or pain awakening patient from sleep
• Fever
• Family history of inflammatory bowel disease or colorectal cancer

Step 3: Perform Baseline Laboratory Testing

All patients with suspected IBS require the following initial tests: 1

Test	Purpose	Interpretation
Complete blood count	Exclude anemia and inflammation	Normal in IBS; anemia suggests IBD [3,4]
C-reactive protein or ESR	Screen for inflammation	Normal in IBS; elevated in IBD (though 20% of active Crohn's have normal CRP) [2]
Coeliac serology (IgA tissue transglutaminase + total IgA)	Exclude celiac disease	Sensitivity >90%; use IgG-based testing if IgA-deficient [2]
Faecal calprotectin (in patients <45 years with diarrhea)	Exclude inflammatory bowel disease	<100 μg/g supports IBS; >100-150 μg/g suggests IBD [1,4]

Additional testing based on clinical context: 2

• Stool microscopy for Giardia if diarrhea-predominant
• Lactose breath testing only if patient consumes >280 mL (0.5 pint) milk daily
• Consider bile acid malabsorption testing (SeHCAT scan or serum 7α-hydroxy-4-cholesten-3-one) in IBS-D with atypical features such as nocturnal diarrhea or prior cholecystectomy 1

Step 4: Tests NOT to Perform

Avoid the following in typical IBS without alarm features: 1, 2

• Colonoscopy in patients <45 years with typical symptoms and no alarm features
• Ultrasound (detects incidental findings unrelated to symptoms)
• Hydrogen breath testing for small intestinal bacterial overgrowth
• Food elimination diets based on IgG antibodies
• Serologic tests marketed for IBS diagnosis (sensitivity <50%)
• Testing for exocrine pancreatic insufficiency
• Stool ova and parasites (except Giardia) unless travel to endemic areas

Management Strategy

Establish Therapeutic Relationship

Provide a positive diagnosis with clear explanation and reassurance of benign prognosis. 1 This approach improves quality of life, reduces healthcare visits, and enhances treatment adherence. 1 Listen to patient concerns and address their specific fears about the condition. 1

First-Line Non-Pharmacological Interventions

Recommend regular exercise to all patients. 1 Strong recommendation despite weak quality evidence. 1

Implement dietary modifications in stepwise fashion: 1

1. Initial dietary advice (first-line): 1

   • Identify and eliminate common triggers (excessive caffeine, alcohol)
   • Ensure adequate hydration
   • Regular meal patterns with adequate time for defecation
   • Avoid food fads or unnecessary restrictions

2. Soluble fiber supplementation: 1

   • Use ispaghula or similar soluble fiber
   • Start low dose (3-4 g/day) and build gradually to avoid bloating
   • Avoid insoluble fiber (wheat bran) as it may worsen symptoms
   • Strong recommendation with moderate quality evidence

3. Low-FODMAP diet (second-line): 1

   • Implement only under supervision of trained dietitian
   • Reintroduce FODMAPs according to tolerance
   • Weak recommendation with very low quality evidence

Do not recommend gluten-free diets. 1

Pharmacological Management by Predominant Symptom

For abdominal pain: 1

• Antispasmodics (hyoscyamine, dicyclomine) as first-line agents
• Consider tricyclic antidepressants if pain persists

For IBS with diarrhea (IBS-D): 5

• Loperamide for stool frequency and urgency (over-the-counter)
• Bile acid sequestrants if bile acid malabsorption suspected
• FDA-approved prescription options: rifaximin, eluxadoline, alosetron

For IBS with constipation (IBS-C): 6

• Osmotic laxatives as first-line
• FDA-approved prescription options: linaclotide, lubiprostone, plecanatide

Probiotics may be considered for global symptoms and pain, though no specific strain can be recommended. 1

Follow-Up and Referral Criteria

Review patients 4-6 weeks after initiating therapy to assess response and adjust treatment. 2

Refer to gastroenterology when: 1

• Diagnostic doubt exists
• Symptoms are severe or refractory to first-line treatments after 3-6 weeks
• Patient requests specialist opinion
• New alarm features develop
• Patient reaches age 45 years with ongoing symptoms

Colonoscopy becomes indicated if: 1

• Alarm symptoms or signs develop
• IBS-D with atypical features suggesting microscopic colitis (female sex, age ≥50 years, autoimmune disease, nocturnal/severe watery diarrhea, duration <12 months, weight loss, use of NSAIDs or PPIs)

Critical Pitfalls to Avoid

Do not perform exhaustive serial testing in patients with typical IBS symptoms and no alarm features—this increases anxiety without diagnostic benefit. 1, 2

Do not rely solely on patient-reported food intolerances without objective testing, as this leads to unnecessary dietary restrictions. 2

Do not assume normal CRP excludes IBD—approximately 20% of patients with active Crohn's disease have normal inflammatory markers. 2

Do not delay colonoscopy in patients ≥45 years with new-onset symptoms, regardless of symptom pattern. 1

Do not attribute all symptoms to IBS in established patients—new alarm features require re-evaluation for organic disease. 3

Recognize the substantial placebo response (50%) in IBS treatment, which typically wears off over subsequent months. 1