What is the appropriate initial workup for a patient with suspected Crohn's disease?

Initial Workup for Suspected Crohn's Disease

The initial workup for suspected Crohn's disease should begin with comprehensive laboratory testing followed by ileocolonoscopy with biopsies, then proceed to small bowel imaging with MR enterography as the preferred first-line modality. 1

Clinical Assessment

Obtain a detailed history focusing on:

• Stool characteristics: frequency, consistency, presence of blood 1
• Constitutional symptoms: fever, weight loss, malaise 1, 2
• Abdominal pain patterns: chronic or intermittent 1, 2
• Extraintestinal manifestations: arthritis/arthralgia, eye symptoms (uveitis), skin findings (erythema nodosum, pyoderma gangrenosum) 1
• Perianal disease: fistulas, abscesses, skin tags 1, 3
• Medication history: particularly NSAIDs (must be withdrawn 4 weeks before capsule endoscopy if planned) 1
• Smoking status and family history of IBD 1

Physical examination must include:

• Vital signs, weight, and assessment for fluid depletion 1
• Abdominal examination for tenderness, masses, or distension 1
• Mandatory perianal examination to detect fistulas or abscesses 1, 3

Initial Laboratory Investigations

Order the following baseline tests: 1, 2

• Complete blood count (assess for anemia, elevated platelets, leukocytosis) 1, 4
• Inflammatory markers: ESR and/or CRP 1, 2
• Comprehensive metabolic panel (U&Es, liver function tests) 1
• Fecal calprotectin: levels >100 mg/g predict positive findings (43%), >200 mg/g provide higher yield (65%) 2
• Stool studies including culture and Clostridium difficile toxin 1
• Nutritional markers: vitamin B12, folate, albumin, vitamin D 5

Key diagnostic predictors: The combination of anemia with elevated inflammatory markers (particularly elevated platelet count) significantly increases diagnostic yield 4

Endoscopic Evaluation

Ileocolonoscopy with biopsies is the first-line diagnostic procedure and should be performed when clinically safe: 1, 2

• Intubate the terminal ileum and obtain biopsies even if macroscopically normal 1
• Take segmental biopsies throughout the colon 1, 2
• Document findings using standardized scoring systems 1

Typical endoscopic findings include: 6

• Non-continuous (skip) lesions 1
• Longitudinal ulcers and cobblestone appearance 6
• Aphthous ulcerations arranged longitudinally 6

Histologic features to identify: 1, 6

• Focal, asymmetric, patchy chronic inflammation 1, 6
• Focal crypt irregularity 6
• Non-caseating granulomas (pathognomonic but not always present) 1, 6

Small Bowel Imaging

MR enterography is the preferred first-line imaging modality: 1, 2

• Does not expose patients to ionizing radiation 1, 2
• Requires oral contrast (900-1,500 mL over 45-60 minutes) for adequate bowel distention 1
• Coverage must include the perineum to detect perianal disease 1
• Assesses transmural inflammation, strictures, and extraluminal complications 1

CT enterography is appropriate when: 1, 2

• MRE is unavailable 2
• Emergency setting requiring rapid acquisition 2
• Patient has contraindications to MRI 1

Small bowel follow-through remains an option but is inferior to cross-sectional imaging 1, 5

Abdominal Radiography

Plain abdominal X-ray should be obtained in patients with suspected severe disease: 1

• Excludes colonic dilatation 1
• May reveal small bowel dilatation or right iliac fossa mass 1
• Helps assess disease extent in acute presentations 1

Advanced Diagnostic Modalities

Small Bowel Capsule Endoscopy (SBCE)

Reserve capsule endoscopy for patients with high clinical suspicion but negative ileocolonoscopy and imaging: 1, 2

Selection criteria for SBCE: 1

• Typical symptoms (chronic abdominal pain, chronic diarrhea, weight loss) PLUS
• Extraintestinal manifestations OR elevated inflammatory markers/fecal calprotectin OR abnormal imaging 1

Critical safety measure: Use a patency capsule first in patients with: 1, 2

• Obstructive symptoms 1, 2
• History of small bowel resection 1
• Known stenosis 1

Important limitation: SBCE has high negative predictive value but lower specificity than cross-sectional imaging 1

Ultrasound

Intestinal ultrasound (IUS) in skilled hands can identify thickened bowel loops and complications but is operator-dependent 1

Common Pitfalls to Avoid

• Do not skip perianal examination: 15-25% of pediatric patients and 13-27% of all patients have perianal disease at presentation 1, 3
• Withdraw NSAIDs 4 weeks before capsule endoscopy: Drug-induced lesions can mimic Crohn's disease 1
• Do not perform capsule endoscopy without patency assessment in patients with obstructive symptoms or known strictures—risk of capsule retention 1, 2
• Ensure imaging includes the perineum: Perianal disease may be occult on physical examination 1, 3
• Do not rely on single test: Diagnosis requires integration of clinical, endoscopic, histologic, and radiologic findings 1, 7

Differential Diagnosis Considerations

Rule out infectious causes, particularly in endemic areas: 1, 6

• Intestinal tuberculosis (more prevalent in Korea and endemic regions) 6
• Behçet's disease 1, 6
• Ischemic colitis 8
• Other causes of granulomatous inflammation (lymphoma, vasculitis) 1

Algorithmic Summary

1. Clinical assessment → detailed history focusing on GI symptoms, extraintestinal manifestations, perianal disease, plus mandatory perianal examination 1, 3
2. Laboratory workup → CBC, ESR/CRP, metabolic panel, fecal calprotectin, stool studies 1, 2, 4
3. Ileocolonoscopy with biopsies → first-line diagnostic procedure with terminal ileal intubation 1, 2
4. MR enterography → preferred small bowel imaging (or CT enterography if MRI unavailable/contraindicated) 1, 2
5. Capsule endoscopy → only if steps 3-4 are negative/inconclusive AND clinical suspicion remains high with supporting features 1, 2