Diagnostic Approach to Inflammatory Bowel Disease

Initial Screening Tests

The European Crohn’s and Colitis Organisation recommends fecal calprotectin as the initial screening test for inflammatory bowel disease, with a sensitivity of 93-95% and specificity of 91-96% for differentiating IBD from non-IBD diagnoses 1, 2
Values <50 μg/g are reassuring and point toward consideration of a non-IBD etiology for persisting symptoms, according to the American Gastroenterological Association 2

The American College of Gastroenterology recommends complete blood count (CBC) to assess for anemia and inflammatory markers, with a strength of evidence rated as high 3, 1
C-reactive protein (CRP) is recommended as a marker of systemic inflammation, though approximately 15-20% of patients with active IBD may have normal CRP levels, as stated by the Crohn’s and Colitis Foundation 1, 4, 2

The American Society for Gastrointestinal Endoscopy recommends ileocolonoscopy with visualization of the terminal ileum and all colonic segments, with biopsies from both affected and normal-appearing areas, as the reference standard for IBD diagnosis 1, 6, 5
Biopsies should be taken from every segment including the rectum to document skip lesions and support differential diagnosis between Crohn's disease and ulcerative colitis, according to the World Gastroenterology Organisation 1, 5

The European Society of Gastrointestinal and Abdominal Radiology recommends cross-sectional imaging (MR enterography preferred, or CT enterography) to assess small bowel involvement, disease extent, and complications if IBD is confirmed or strongly suspected 1, 7, 5
MR enterography or CT enterography is superior to traditional fluoroscopic studies for detecting active disease and extramural complications, as stated by the American College of Radiology 7, 6