Crohn's Disease in Adults

Diagnosis, treat-to-target strategy, biologic selection, surgery, and long-term monitoring — ACG 2025 Guidelines.

Diagnosis & Classification

Montreal classification, biomarkers

Diagnosing Crohn's Disease

CD is a transmural, skip-lesion inflammatory disease that can affect any part of the GI tract. Diagnosis requires integrated clinical, endoscopic, imaging, and histologic evidence.

Montreal Classification (Location & Behavior)

Location (L)

L1Terminal ileum

L2Colon only

L3Ileocolon

L4Upper GI (add to L1–L3)

Behavior (B)

B1Non-stricturing, non-penetrating (inflammatory)

B2Stricturing

B3Penetrating (fistulizing)

+pPerianal disease modifier

CRP / ESR

Elevated in active disease; CRP more sensitive

Fecal Calprotectin

>250 μg/g suggests active intestinal inflammation. Use to monitor mucosal healing.

Fecal Lactoferrin

Alternative to calprotectin; good sensitivity for intestinal inflammation

Differentiating CD from UC

Key CD features: skip lesions, transmural inflammation, granulomas, perianal disease, small bowel involvement, rectal sparing. UC: continuous colonic involvement starting at rectum, no small bowel involvement (except backwash ileitis), no granulomas.

Lichtenstein GR et al. ACG Clinical Guideline: Management of Crohn's Disease in Adults. Am J Gastroenterol. 2025.