What are the diagnostic tests and procedures for Crohn's (Chronic Regional Ileitis) disease?

Diagnostic Tests and Procedures for Crohn's Disease

The primary diagnostic approach for suspected Crohn's disease should include ileocolonoscopy with biopsies as the first-line investigation, followed by cross-sectional imaging (preferably MR enterography) to assess small bowel involvement. 1

Initial Diagnostic Workup

First-Line Investigations

• Ileocolonoscopy with biopsies: Gold standard for diagnosis
  • Multiple biopsies should be taken from both inflamed and uninflamed segments 1, 2
  • At least two biopsies from terminal ileum and at least four from different colonic segments 1
  • Allows direct visualization of mucosal lesions and collection of tissue for histological confirmation

Laboratory Tests

• Complete blood count (anemia assessment: Hb <13 g/dL for men, <12 g/dL for women)
• C-reactive protein (CRP) - values <5 mg/L suggest absence of active inflammation
• Fecal calprotectin - most sensitive non-invasive marker
  • Values <150 μg/g rule out active inflammation with high confidence
  • Values >250 μg/g have higher specificity (74%) for active inflammation 2
• Liver profile, albumin, iron studies, renal function tests

Imaging Modalities

Small Bowel Imaging

• MR Enterography (MRE): Preferred first-line imaging for small bowel assessment 1

  • No radiation exposure
  • Excellent for detecting transmural inflammation and extraluminal complications
  • Requires oral contrast ingestion (900-1,500 mL over 45-60 minutes) 1

• CT Enterography (CTE): Alternative to MRE

  • Faster acquisition time (<2 seconds)
  • High diagnostic performance (sensitivity >80%, specificity >85%) 1
  • Disadvantage: Radiation exposure

• Small Bowel Ultrasound (SBUS)

  • Non-invasive, no radiation
  • Similar value to MRE for monitoring transmural healing 1
  • Dependent on operator expertise and patient body habitus

Advanced Diagnostic Options

• Small Bowel Capsule Endoscopy

  • Consider when small bowel Crohn's is suspected despite normal/inconclusive investigations 1
  • Superior to barium follow-through and similar to CT/MRE
  • Use patency capsule first in patients with obstructive symptoms 1

• Balloon-Assisted Enteroscopy

  • Allows biopsy collection from areas beyond reach of conventional endoscopy
  • Consider when diagnostic uncertainty exists and tissue sampling would alter treatment approach

Diagnostic Algorithm

1. Initial Assessment:

   • If fecal calprotectin <150 μg/g AND CRP <5 mg/L: Low probability of Crohn's disease
   • If fecal calprotectin >150 μg/g OR CRP >5 mg/L: Proceed to ileocolonoscopy 2

2. Endoscopic Evaluation:

   • Perform ileocolonoscopy with multiple biopsies
   • Look for characteristic findings: discontinuous lesions, longitudinal ulcers, cobblestone appearance, strictures, fistulae 2
   • Use standardized endoscopic scoring systems (e.g., Simple Endoscopic Score for Crohn's Disease) 1

3. Cross-Sectional Imaging:

   • MRE or CTE to assess small bowel involvement (prefer MRE to avoid radiation)
   • Particularly important when terminal ileum cannot be intubated during colonoscopy

4. Additional Investigations:

   • Upper GI endoscopy only if upper GI symptoms are present 1
   • Perianal examination and imaging if perianal symptoms exist

Common Pitfalls and Caveats

• Incomplete colonoscopy: Terminal ileum intubation failure can miss isolated ileal disease 2
• Inadequate biopsies: Taking too few samples or only from visibly inflamed areas reduces diagnostic yield
• Relying solely on endoscopy: Up to 20% of patients have isolated proximal small bowel disease beyond the reach of ileocolonoscopy 1
• Misinterpreting imaging: Inadequate bowel preparation can result in false negatives 2
• Differential diagnosis challenges: Crohn's disease can mimic intestinal tuberculosis, Behçet's enterocolitis, and other conditions 3
• Disease monitoring: Serial measurements of fecal calprotectin are more reliable than absolute values for monitoring disease activity 1

By following this systematic diagnostic approach, clinicians can accurately diagnose Crohn's disease, determine disease extent and severity, and guide appropriate treatment decisions to improve patient outcomes.