A 72-year-old woman presents with painless per rectum bleeding for 3 days. She has no abdominal pain, no weight loss, and no change in bowel habits. Hemoglobin is 10.2 g/dL. Upper GI endoscopy is normal. Which investigation is most appropriate to localize the source of lower GI bleeding?

Explanation

## Investigation of Choice in Lower GI Bleeding **Key Point:** Colonoscopy is the first-line investigation for lower gastrointestinal bleeding — it is both diagnostic and therapeutic with high sensitivity and specificity. ### Diagnostic Algorithm for Lower GI Bleeding ```mermaid flowchart TD A[Lower GI bleeding]:::outcome --> B{Hemodynamically stable?}:::decision B -->|Yes| C[Colonoscopy]:::action B -->|No| D[Resuscitate + stabilize]:::action D --> E[Colonoscopy when stable]:::action C --> F[Source identified?]:::decision F -->|Yes| G[Therapeutic intervention]:::action F -->|No| H[Consider other imaging]:::decision H --> I[Capsule endoscopy or CTA]:::action ``` ### Why Colonoscopy is First-Line 1. **High diagnostic yield**: 70–90% sensitivity for identifying bleeding source 2. **Common sources identified**: Hemorrhoids, diverticulosis, angiodysplasia, polyps, inflammatory bowel disease 3. **Therapeutic capability**: Can perform hemostasis (injection, cautery, clipping, banding) 4. **Timing**: Can be performed urgently in stable patients 5. **Safety**: Well-tolerated with low complication rate in appropriate patient selection ### Clinical Context In this 72-year-old with: - **Painless per rectum bleeding** (suggests lower GI source) - **Normal upper GI endoscopy** (excludes upper GI source) - **Hemodynamic stability** (permits safe colonoscopy) - **No alarm features** (no weight loss, no change in bowel habits) Colonoscopy is the diagnostic and therapeutic investigation of choice. ### Comparison of Lower GI Investigations | Investigation | Indication | Sensitivity | Therapeutic? | Limitation | | --- | --- | --- | --- | --- | | **Colonoscopy** | First-line for stable bleeding | 70–90% | Yes | Requires bowel prep, cannot visualize proximal small bowel | | Meckel's scan | Suspected Meckel's diverticulum | 85% | No | Low yield in adult bleeding, requires clinical suspicion | | Capsule endoscopy | Obscure GI bleeding, negative colonoscopy | 60–70% | No | Cannot treat, small bowel source only | | CT enterography | Suspected small bowel source, unstable patient | 70–80% | No | Radiation, non-therapeutic | **High-Yield:** Colonoscopy should be performed within 24 hours of presentation in stable patients with lower GI bleeding. Bowel preparation (polyethylene glycol or sodium phosphate) is essential for adequate visualization. **Clinical Pearl:** In a patient with brisk lower GI bleeding and hemodynamic instability, consider urgent CT angiography to localize bleeding before colonoscopy; however, in stable patients like this one, colonoscopy is preferred. ### Why Other Investigations Are Not First-Line - **Meckel's scan**: Only 10–15% of Meckel's diverticula bleed; indicated only if clinical suspicion is high and colonoscopy is negative - **Capsule endoscopy**: Reserved for obscure GI bleeding (recurrent bleeding after negative colonoscopy and upper GI endoscopy) - **CT enterography**: Better for detecting small bowel sources but not therapeutic; reserved for cases where colonoscopy is negative or contraindicated