How should I diagnose and initially manage an adult with suspected irritable bowel syndrome who has no red‑flag symptoms?

Diagnosis and Initial Management of IBS Without Red-Flag Symptoms

Make a positive, symptom-based diagnosis of IBS in primary care when abdominal pain occurs at least 1 day per week for the last 3 months, is relieved by defecation or associated with changes in stool frequency or consistency, and perform only limited baseline investigations (full blood count, C-reactive protein or ESR, coeliac serology, and faecal calprotectin if age <45 with diarrhoea) to exclude organic disease. 1, 2

Diagnostic Approach

Make a Positive Diagnosis Based on Symptoms

• IBS is not a diagnosis of exclusion—diagnose it positively when characteristic symptoms are present without alarm features 2, 1
• The NICE definition is more pragmatic for primary care: abdominal pain or discomfort with altered bowel habit for at least 6 months, without alarm symptoms 1
• Rome IV criteria require recurrent abdominal pain at least 1 day per week in the last 3 months, with two or more of: pain relieved by defecation, pain associated with change in stool frequency, or pain associated with change in stool consistency 2, 1

Key Diagnostic Features Supporting IBS

• Abdominal pain relieved by defecation is the hallmark symptom 3, 4
• Symptoms present for more than 6 months with fluctuating course 3, 1
• Normal physical examination with typical symptoms allows safe diagnosis in primary care 3, 4
• Female predominance (2:1 ratio), peak age 20s-30s 3, 4
• Associated non-GI symptoms: lethargy, poor sleep, backache, urinary frequency 3, 4
• Bloating and visible abdominal distension (though not required for diagnosis) 1
• Frequent consultations for non-gastrointestinal symptoms and previous medically unexplained symptoms 1

Baseline Investigations Required

Perform These Tests in ALL Patients at First Presentation

• Full blood count 1, 2
• C-reactive protein or erythrocyte sedimentation rate 1, 2
• Coeliac serology 1, 2
• Faecal calprotectin only if diarrhoea present AND age <45 years 1, 2

Do NOT Perform Extensive Testing

• Avoid exhaustive testing in typical IBS without alarm features, as this increases patient anxiety without benefit 3
• IgG food antibody testing is not recommended 1
• Colonoscopy is not indicated for typical IBS symptoms without alarm features 1, 3
• Once functional diagnosis is established, the incidence of new organic diagnoses is extremely low 1

Initial Management Strategy

First Consultation: Establish Therapeutic Relationship

• Spend 2 minutes of active listening at the beginning—this gives patients confidence in subsequent care decisions 1
• Make a positive diagnosis and explain symptoms in language the patient understands 1
• Provide reassurance of benign prognosis 1
• Ask what the patient's fears and beliefs are—simply listening reduces anxiety 1
• Explain there is no cure for IBS; treatments aim to improve quality of life 1

First-Line Non-Pharmacological Management

Lifestyle modifications (implement all of these):

• Advise regular physical exercise 1, 2
• Establish regular times for defecation 2
• Implement proper sleep hygiene 2
• Identify and address stress factors that aggravate symptoms 1

Dietary interventions (start with these):

• Provide standard first-line dietary advice: identify food fads or deficiencies, assess fibre intake 1
• Start soluble fibre supplementation (ispaghula) for global symptoms and abdominal pain 1
• Avoid insoluble fibre (wheat bran) as it may exacerbate symptoms 1
• Consider low FODMAP diet if first-line measures fail 2

Pharmacological Management (Symptom-Targeted)

• Antispasmodic drugs for abdominal pain 5
• Test one drug at a time with predefined timepoint for effectiveness evaluation 6
• Select medications based on predominant bowel habit (IBS-C, IBS-D, IBS-M) 2, 7

Psychological Interventions (Consider Early)

• Cognitive behavioural therapy, gut-directed hypnotherapy, or mindfulness-based stress reduction should be considered early, particularly with psychological comorbidity 2, 1

Follow-Up and Reassessment

• Reassess after 4-6 weeks of initial treatment 2
• Evaluate both gastrointestinal and psychological symptoms 2
• Adjust treatment based on symptom evolution 2
• Expect substantial placebo response (50%) initially, though this wears off over following months 1

Critical Pitfalls to Avoid

• Do not miss new alarm features in patients with established IBS diagnosis—these require re-evaluation 3
• Do not perform colonoscopy for typical IBS without alarm features in patients <45 years with chronic symptoms (>2 years) and normal initial tests 3
• Do not ignore that colorectal cancer risk is increased immediately after IBS diagnosis due to overlapping symptoms—maintain appropriate vigilance in first 3 months 3
• Do not attribute everything to IBS once diagnosis is made—remain alert to new developments 3