Diagnostic Approach to Lower Gastrointestinal Bleeding

Initial Assessment and Risk Stratification

The American College of Gastroenterology recommends calculating the shock index (heart rate ÷ systolic blood pressure) immediately upon presentation to assess hemodynamic status 1, 2
A shock index >1 indicates hemodynamic instability, mandating urgent CT angiography rather than routine endoscopy 1, 2
For hemodynamically stable patients, the Oakland score should be applied to determine the need for hospital admission or outpatient investigation 1

The European Society of Gastrointestinal Endoscopy recommends digital rectal examination to confirm blood in stool and exclude anorectal pathology 1, 3
Complete blood count, serum electrolytes, BUN, creatinine, coagulation assessment, and inflammatory markers should be obtained in all patients 3, 4
Blood typing and cross-matching are necessary for patients with signs of severe bleeding 3
Stool testing for Clostridium difficile should be performed in all new presentations of diarrhea, regardless of antibiotic history 4

CT angiography is the recommended initial imaging modality for hemodynamically unstable patients, with a sensitivity of 79-95% and specificity of 95-100% 1, 2, 5
Colonoscopy is the primary diagnostic modality for stable patients, but should not be performed as the initial approach in hemodynamically unstable patients 1, 7

Restrictive transfusion thresholds should be used, with a hemoglobin trigger of 70 g/L and target of 70-90 g/L for patients without cardiovascular disease 1, 2, 5
Warfarin should be interrupted immediately in patients with unstable bleeding, and reversed with prothrombin complex concentrate and vitamin K 1, 2

Mortality in lower GI bleeding is generally related to comorbidity rather than exsanguination, with an overall in-hospital mortality of 3.4% 1