What are the causes of lower gastrointestinal (GI) bleeding?

Causes of Lower Gastrointestinal Bleeding

Diverticulosis is the single most common cause of lower GI bleeding, accounting for 21-41% of all cases, followed by angiodysplasia (3-40%), colorectal malignancy/polyps (6-27%), inflammatory bowel disease, anorectal disease, and ischemic colitis. 1

Primary Etiologies by Frequency

Most Common Causes

• Diverticulosis represents 30-41% of lower GI bleeding cases and is the leading etiology, with prevalence reaching 50% in patients over 60 years of age 2, 1
• Diverticular bleeding characteristically presents as painless bleeding, which distinguishes it from inflammatory or ischemic causes 1
• Approximately 75-90% of diverticular bleeding episodes stop spontaneously, particularly in patients requiring <4 units of blood transfusion over 24 hours 1

Vascular Lesions

• Angiodysplasia accounts for 3-40% of cases and represents the second most common cause after diverticulosis 1
• Vascular ectasias increase in frequency with advanced age, similar to diverticular disease 3

Neoplastic Causes

• Colorectal malignancy and polyps account for 6-27% of lower GI bleeding cases 1
• These typically present with chronic, intermittent bleeding rather than acute massive hemorrhage 1
• Approximately 40% of rectal carcinomas are palpable during digital rectal examination 2

Inflammatory and Ischemic Causes

• Inflammatory bowel disease (including Crohn's disease and ulcerative colitis) represents a significant cause, particularly in younger patients 2
• Ischemic colitis and infectious colitis are important considerations, especially in elderly patients with cardiovascular comorbidities 4
• Radiation proctitis can occur 9 months to 4 years after pelvic radiation therapy for prostatic or gynecologic malignancy 2

Anorectal Pathology

• Hemorrhoids, anal fissures, and anorectal varices are common causes, particularly in patients with portal hypertension 2
• Portal hypertension can cause lower GI bleeding through clinically obvious anorectal varices or obscure ectopic varices in the small or large bowel 2

Small Bowel Sources

• Small intestinal sources account for 0.7-9% of cases presenting with severe hematochezia 5
• Small bowel causes include arteriovenous malformations, Meckel's diverticula, small bowel tumors, and Crohn's disease 4, 3

Critical Diagnostic Pitfall

Approximately 10-15% of patients presenting with acute severe hematochezia actually have an upper GI source identified on upper endoscopy, highlighting the importance of excluding upper GI bleeding before attributing symptoms to lower GI pathology 5

Age-Related Considerations

• Advanced age is the strongest risk factor for lower GI bleeding, with both diverticulosis and angiodysplasia increasing dramatically in patients over 60-70 years 2, 1
• Colonic diverticula or angiodysplasia are more likely causes in persons over 70 years of age 2

Medication-Associated Bleeding

• NSAID use is a critical risk factor that must be elicited in the medication history 2, 3
• Anticoagulant and antiplatelet use in the elderly population has resulted in increased incidence of acute diverticular bleeding 6
• Coagulopathy with INR ≥1.5 independently predicts severe diverticular hemorrhage and requires correction with fresh frozen plasma and vitamin K 1

Less Common but Important Causes

• Stress ulcers in the colon can occur in critically ill patients 2
• Surgical anastomoses may bleed in postoperative patients 2
• Post-polypectomy bleeding following colonoscopic polypectomy 3