What is the appropriate workup for suspected Irritable Bowel Syndrome (IBS)?

From the Guidelines

The appropriate workup for suspected Irritable Bowel Syndrome (IBS) includes a full blood count, C reactive protein or erythrocyte sedimentation rate, coeliac serology, and, in patients <45 years of age with diarrhoea, a faecal calprotectin to exclude inflammatory bowel disease.

Initial Evaluation

• A thorough medical history and physical examination should be performed to identify any alarm symptoms or signs, such as weight loss, bleeding, or abdominal masses, which may indicate a more serious underlying condition 1.
• The National Institute for Health and Care Excellence guideline definition of IBS should be used to guide the diagnosis, which includes abdominal pain or discomfort, in association with altered bowel habit, for at least 6 months, in the absence of alarm symptoms or signs 1.

Laboratory Tests

• Full blood count: to rule out anemia or other blood disorders 1.
• C reactive protein or erythrocyte sedimentation rate: to assess for inflammation 1.
• Coeliac serology: to exclude celiac disease, a common cause of chronic diarrhea 1.
• Faecal calprotectin: in patients <45 years of age with diarrhoea, to exclude inflammatory bowel disease 1.

Additional Tests

• Colonoscopy: should not be performed routinely in patients with IBS, but may be considered in patients with alarm symptoms or signs, or those with symptoms suggestive of IBS with diarrhoea who have atypical features and/or relevant risk factors 1.
• 23-seleno-25-homotaurocholic acid scanning or serum 7α-hydroxy-4-cholesten-3-one: may be considered in patients with symptoms suggestive of IBS with diarrhoea, but with atypical features such as nocturnal diarrhoea, or a prior cholecystectomy, to exclude bile acid malabsorption 1.

Referral to Secondary Care

• Referral to gastroenterology in secondary care is warranted where there is diagnostic doubt, in patients with symptoms that are severe, or refractory to first-line treatments, or where the individual patient requests a specialist opinion 1.

From the Research

Diagnostic Approach for Irritable Bowel Syndrome (IBS)

The diagnosis of IBS is primarily based on symptom-based diagnostic criteria, clinical examinations, and laboratory investigations. The following steps can be taken to diagnose IBS:

• Clinical assessment of symptoms, including abdominal pain, changes in stool form or frequency, and associated symptoms such as bloating and distension 2, 3, 4, 5, 6
• Use of symptom-based diagnostic criteria, such as the Rome IV criteria, to increase the likelihood of identifying IBS 2, 3, 4, 5, 6
• Laboratory tests, including complete blood count (CBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), to rule out other conditions 2, 3
• Serological testing for coeliac disease, irrespective of the predominant stool form 3
• Faecal calprotectin or a similar marker measurement in patients with diarrhoea aged <45 to exclude possible inflammatory bowel disease 3
• Colonoscopy in patients with alarm symptoms suggestive of colorectal cancer, or in those whose presentation raises suspicion for microscopic colitis 3

Laboratory Investigations

The yield of routine blood tests in suspected IBS is low overall, but normal inflammatory markers may be reassuring 3. The following laboratory investigations are not recommended as part of the routine workup for IBS:

• Routine testing of stool microbiology or faecal elastase 3
• Hydrogen breath tests for lactose malabsorption or small intestinal bacterial overgrowth 3

Special Considerations

Testing for bile acid diarrhoea should be considered for patients with IBS with diarrhoea where available 3. A positive diagnosis of IBS can be made based on symptom-based diagnostic criteria, and exhaustive investigation is not necessary 2, 3, 4, 5, 6.