A 32-year-old man from Delhi presents with a 6-month history of bloody diarrhoea, abdominal pain, and weight loss. Clinical examination reveals pallor and mild abdominal tenderness. Laboratory investigations show haemoglobin 9.2 g/dL, albumin 2.8 g/dL, and elevated inflammatory markers (CRP 8.5 mg/dL, ESR 52 mm/h). Which investigation is most appropriate to confirm the diagnosis of inflammatory bowel disease and determine disease extent?

Explanation

## Investigation of Choice for Diagnosis and Staging of IBD **Key Point:** Colonoscopy with ileoscopy and mucosal biopsies is the gold standard for diagnosis of inflammatory bowel disease. It allows direct visualisation of the mucosa, determination of disease extent, and histological confirmation through biopsies. ### Why Colonoscopy with Ileoscopy and Biopsies? 1. **Diagnostic confirmation**: Histology showing crypt distortion, chronic inflammation, and crypt abscess differentiates IBD from other causes of colitis (infectious, ischaemic, diverticular). 2. **Disease extent**: Determines whether disease is limited to colon (ulcerative colitis) or involves terminal ileum (Crohn's disease). 3. **Severity assessment**: Allows grading of mucosal inflammation (Mayo score for UC, SES-CD for CD). 4. **Baseline documentation**: Essential for future comparison and monitoring. ### Role of Other Investigations | Investigation | Role | Limitation | |---|---|---| | **Colonoscopy + biopsy** | Gold standard for diagnosis and extent | Invasive; cannot assess small bowel beyond terminal ileum | | **Barium enema** | Historical imaging; poor mucosal detail | Inferior to endoscopy; radiation exposure; cannot obtain biopsies | | **CT enterography** | Assesses transmural disease, complications | Not first-line for diagnosis; better for complications (fistula, abscess) | | **Faecal calprotectin** | Non-invasive biomarker; good for surveillance | Elevated in many conditions; not diagnostic; cannot assess extent | **Clinical Pearl:** In a patient with suspected IBD presenting with bloody diarrhoea and systemic signs, colonoscopy is mandatory to rule out infectious colitis (especially *Clostridium difficile*, shigella, salmonella) before starting immunosuppression. **High-Yield:** The combination of clinical features (bloody diarrhoea, weight loss, elevated CRP/ESR) + colonoscopic findings (continuous inflammation, loss of haustra) + histology (chronic inflammation, crypt distortion) = definitive diagnosis of ulcerative colitis. Ileoscopy differentiates from Crohn's disease. **Mnemonic: BIOPSY** — **B**iopsy confirms diagnosis, **I**leoscopy determines extent, **O**bserves mucosal pattern, **P**rovides severity score, **S**amples for histology, **Y**ields gold standard diagnosis.