What diagnostic steps and treatments should be considered when suspecting inflammatory bowel disease (IBD)?

Diagnostic Approach for Suspected Inflammatory Bowel Disease

When suspecting inflammatory bowel disease (IBD), a comprehensive diagnostic workup should include laboratory testing, stool studies, endoscopy with biopsies, and imaging studies to confirm the diagnosis and rule out other conditions.

Initial Laboratory Investigations

• Blood tests:

  • Full blood count (to detect anemia, leukocytosis, thrombocytosis) 1
  • C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) (inflammatory markers) 2, 1
  • Liver function tests and renal function tests 2, 1
  • Serum albumin (to assess nutritional status) 1
  • Coeliac screen 2

• Stool studies:

  • Fecal calprotectin (key biomarker for intestinal inflammation) 2
  • Stool cultures and Clostridium difficile toxin assay 2, 1
  • Tests for other infectious pathogens 2, 1

Endoscopy and Biopsy

• Ileocolonoscopy with biopsies is the cornerstone diagnostic test 1

  • At least 2 biopsies from each segment (terminal ileum, different colonic segments, and rectum) 2, 1
  • Biopsies should be taken from both inflamed and uninflamed areas 2
  • Histological features to look for include:
    • Basal plasmacytosis (diagnostic feature distinguishing IBD from infection) 2
    • Architectural changes and distribution of inflammation 2
    • Crypt distortion, branching, and atrophy 2

• Flexible sigmoidoscopy may be sufficient in acute severe colitis to avoid perforation risk 1

Imaging Studies

• MR enterography is preferred over CT due to absence of radiation, especially in young patients 1
• Contrast-enhanced CT scan can assess extra-luminal complications when needed 1
• Intestinal ultrasound can identify thickened bowel loops and assess disease activity 1
• Small bowel capsule endoscopy for patients with normal ileocolonoscopy but persistent suspicion of Crohn's disease 1

Diagnostic Algorithm

The British Society of Gastroenterology 2 recommends the following approach for patients aged 16-40 with new lower gastrointestinal symptoms (>4 weeks) where IBD is suspected:

1. For patients with rectal bleeding plus any of: abdominal pain, change in bowel habit, weight loss, or iron deficiency anemia:

   • Measure fecal calprotectin (not appropriate if NSAID use in past 6 weeks)

2. Interpret fecal calprotectin results:

   • <100 μg/g: IBS likely, treat as IBS in primary care
   • 100-250 μg/g: Consider repeat testing or routine referral to gastroenterology

   • 250 μg/g: Refer urgently to gastroenterology

3. All patients should have:

   • Full blood count, urea & electrolytes, CRP, coeliac screen
   • Stool culture when appropriate

Special Considerations

• Exclude infectious causes before confirming IBD diagnosis 1
• Assess for extraintestinal manifestations which can affect joints, skin, eyes, liver, and other organs 3
• Consider early-onset IBD in children under 5 years as it may suggest underlying immune deficiencies 2
• Evaluate for IBD mimics if symptoms are not responding to standard IBD treatment, including:
  • Infectious etiologies (viral, bacterial, mycobacterial, fungal, protozoal)
  • Vascular causes
  • Autoimmune conditions
  • Drug-induced processes
  • Small intestinal bacterial overgrowth
  • Bile acid malabsorption 4

Common Pitfalls to Avoid

1. Relying solely on symptoms without objective evidence of inflammation (symptoms may be due to irritable bowel syndrome or other functional disorders) 2

2. Making treatment decisions based on clinical symptoms alone without confirming active inflammation through biomarkers, endoscopy, or imaging 2

3. Misinterpreting intermediate fecal calprotectin values (100-250 μg/g) - these require clinical context and possibly repeat testing 2

4. Failing to consider IBD mimics when patients don't respond to standard IBD therapy 4

5. Overlooking the need for vaccination assessment before starting immunosuppressive therapy 2

By following this systematic diagnostic approach, clinicians can effectively diagnose IBD and differentiate it from other conditions with similar presentations, leading to appropriate treatment decisions and better patient outcomes.