What diagnostic tests are used to check for Inflammatory Bowel Disease (IBD)?

Diagnostic Tests for Inflammatory Bowel Disease (IBD)

Ileocolonoscopy with biopsies from both inflamed and uninflamed segments is the cornerstone diagnostic test for suspected IBD, as it allows for direct visualization of the mucosa and collection of tissue samples for histological confirmation. 1

Initial Diagnostic Approach

Clinical and Laboratory Assessment

• History and examination: Focus on stool frequency/consistency, rectal bleeding, abdominal pain, weight loss, fever, and extraintestinal manifestations 1
• Laboratory investigations:
  • Full blood count (FBC)
  • Electrolytes (U&Es)
  • Liver function tests
  • Inflammatory markers: ESR or C-reactive protein (CRP)
  • Stool tests to exclude infectious causes (including C. difficile toxin)
  • Iron studies (ferritin, transferrin saturation) to assess for iron deficiency 1

Endoscopic Evaluation

• Ileocolonoscopy: Gold standard for initial diagnosis 1
  • Multiple biopsies should be taken from:
    • Terminal ileum (at least 2 biopsies)
    • Each colonic segment (at least 2 biopsies per segment)
    • Rectum (at least 2 biopsies)
    • Both inflamed and uninflamed areas 1
  • In acute severe colitis, flexible sigmoidoscopy may be sufficient to avoid perforation risk 1

Histopathological Assessment

• Biopsy handling: Immediate fixation in buffered formalin 1
• Processing: Serial or step sectioning (2-6 sections) to detect focal lesions 1
• Key histological features:
  • UC: Diffuse mucosal inflammation, basal plasmacytosis, crypt distortion, mucin depletion 1
  • CD: Transmural, discontinuous inflammation, focal crypt irregularities, granulomas 1

Additional Diagnostic Tests

Small Bowel Evaluation

• Small bowel capsule endoscopy (SBCE): Consider in patients with:
  • Clinical suspicion of CD with normal ileocolonoscopy
  • Unexplained iron deficiency anemia
  • Elevated fecal calprotectin (>50μg/g) with normal colonoscopy 1
  • Note: Assess risk of retention if stenotic disease is suspected

Cross-Sectional Imaging

• MR enterography: Preferred over CT due to absence of radiation, especially in young patients 1
• Intestinal ultrasound: Non-invasive method to identify thickened bowel loops and assess disease activity 1

Upper GI Endoscopy

• Recommended for CD patients with upper GI symptoms
• Not routinely needed for asymptomatic newly diagnosed adult IBD patients 1

Biomarkers

Fecal Markers

• Fecal calprotectin: Most validated biomarker for IBD 2
  • Helps differentiate IBD from functional disorders
  • Useful for monitoring disease activity
  • Low levels (<50μg/g) make IBD diagnosis unlikely 1

Serological Markers

• pANCA and ASCA: Limited accuracy for differentiating colonic CD from UC 1
• Other antibodies (antiglycan, antimicrobial): Provide minimal additional diagnostic value 1

Diagnostic Pitfalls and Considerations

1. No single reference standard exists for IBD diagnosis - combination of clinical, biochemical, endoscopic, radiological, and histological findings is required 1

2. Exclude infectious causes before confirming IBD diagnosis:

   • Stool testing for common pathogens
   • C. difficile toxin assay
   • Consider travel history for additional testing 1

3. Endoscopic features are not specific:

   • UC: Continuous and confluent colonic involvement with clear demarcation and rectal involvement
   • CD: Discontinuous lesions, strictures, fistulae, and perianal involvement 1

4. Histological diagnosis challenges:

   • Early disease may lack characteristic features
   • Basal plasmacytosis is an early diagnostic feature for UC
   • Crypt distortion may take at least 4 weeks to develop 1

5. Genetic testing for IBD-associated variants is not recommended for diagnosis 1

The diagnostic approach should be systematic and comprehensive, as misdiagnosis can lead to inappropriate treatment and poorer outcomes. When diagnostic uncertainty exists, it's reasonable to repeat endoscopic evaluation after a period of observation.