Evaluation and Management of Lower Gastrointestinal Bleeding

Introduction to Causes and Initial Evaluation

The presence of bright red blood in stool requires a complete colon evaluation, as up to 48% of patients will have significant lesions that change management, including colorectal cancer in 8-19% of cases 1, 2
The American Gastroenterological Association suggests that diverticulosis is the most common cause of lower gastrointestinal bleeding, accounting for 21-41% of cases, particularly in patients over 65 years old 1, 2
Hemorrhoids and anorectal lesions account for 14-28% of cases, including hemorrhoids, anal fissures, and rectal ulcers 1, 2
Polyps and colorectal cancer combined account for 14-37% of cases, with cancer representing 8-19% specifically 1, 2
Ischemic colitis and inflammatory bowel disease account for 11-21% of cases 1, 2
Angiodysplasia accounts for 2-40% of cases, depending on patient age, and is more common in patients over 70 years old 1, 2

Approximately 10-15% of patients presenting with bright red blood per rectum have an upper gastrointestinal source of bleeding, especially if there is hemodynamic instability 2, 3, 4
Factors suggesting an upper source include massive bleeding with hemodynamic instability 2, 3, history of peptic ulcer or portal hypertension 5, use of nonsteroidal anti-inflammatory drugs (NSAIDs) or anticoagulants 5, and elevated urea/creatinine ratio 3

Calculate the shock index (heart rate/systolic blood pressure): a value >1 indicates hemodynamic instability requiring immediate hospital referral 3, 6, 4
Check blood pressure, heart rate, and orthostatic changes 5, 6
Obtain hemoglobin/hematocrit if available 5, 6, 4

Perform digital rectal examination and anoscopy to identify hemorrhoids, fissures, or masses, but never attribute bleeding exclusively to hemorrhoids without complete colon evaluation 2, 7, 6
History of aortic surgery requires immediate hospital evaluation 6
Age over 70 years increases the likelihood of diverticulosis and angiodysplasia 1, 2

First-line: computed tomography angiography (CTA) to rapidly localize the bleeding site without bowel preparation 3, 4
CTA has a sensitivity of 79-95% and specificity of 95-100% for active bleeding 4
If CTA is negative, perform immediate upper endoscopy to exclude an upper gastrointestinal source 3, 4
Avoid colonoscopy as the first option in unstable patients 3, 4

Initiate with direct anorectal examination (anoscopy/proctoscopy) to identify common anorectal causes 3, 4
All patients over 45 years old with rectal bleeding require complete colonoscopy within 2 weeks, regardless of rectal examination findings 6
Flexible sigmoidoscopy alone is inadequate: up to 20 patients out of 217 with bright red blood had proximal lesions, including 8 cancers 6

Age ≥45 years 6
Family history of colorectal cancer 6
Previous polyps or inflammatory bowel disease 6
Coagulopathy (INR >1.5) or thrombocytopenia (<50,000/µL) should be corrected with fresh frozen plasma or platelets before procedures 5

Patients with a history of pelvic radiation may present with radiation proctitis 9 months to 4 years after treatment 5
Anemia due to hemorrhoids is rare (0.5 patients/100,000 population) and responds to hemorrhoidectomy 7
Occult blood in stool should not be attributed to hemorrhoids until the colon is adequately evaluated 7