Differential Diagnosis for Lower GI Bleeding
Common Causes by Frequency
The most common causes of lower GI bleeding are diverticular disease and vascular ectasia (angiodysplasia), followed by ischemic colitis, inflammatory/infectious colitis, colorectal neoplasia, and anorectal pathology. 1
Major Bleeding Sources
Diverticular disease represents the most frequently identified source across clinical series, particularly in older patients 1
Vascular ectasia (angiodysplasia) is the second most common cause and often presents with intermittent bleeding 1
Ischemic colitis should be suspected in patients with severe atherosclerosis, renal failure, or recent hypotensive episodes 2
Inflammatory or infectious colitis including Crohn's disease, ulcerative colitis, and infectious etiologies 1
Colorectal neoplasia including cancer and post-polypectomy bleeding, with cancer being particularly common in patients on warfarin 3, 1
Anorectal Causes
Hemorrhoids are common but rarely cause severe bleeding requiring hospitalization 1
Anal fissures typically present with bright red blood on tissue paper with formed stool 1
Rectal varices should be considered in patients with portal hypertension 1
Small Bowel Sources
Meckel's diverticulum should be considered in young patients with otherwise unexplained lower GI bleeding, diagnosed via radionuclide scan 2, 1
Small bowel Crohn's disease may present as lower GI bleeding 1
Small bowel vascular ectasia can be identified via video capsule endoscopy, which has a diagnostic yield of 55-65% for obscure GI bleeding 2
Small bowel tumors are rare but should be evaluated with push enteroscopy or video capsule endoscopy when upper endoscopy and colonoscopy are negative 2
Risk Factors That Modify Differential
Advanced age is strongly associated with diverticular bleeding and angiodysplasia 1
NSAID use significantly increases risk of bleeding from diverticulosis and angiodysplasia 4, 1
Anticoagulant/antiplatelet therapy is an independent predictor of severe lower GI bleeding and increases likelihood of finding colorectal abnormalities including cancer 3
Severe atherosclerosis or renal failure increases risk of non-occlusive ischemic colitis, which may present fulminantly with colonic infarction requiring urgent surgery 2
Critical Diagnostic Consideration
Always consider an upper GI source in patients with hemodynamic instability (shock index >1), even when presenting with hematochezia, as failure to do so leads to delayed diagnosis and treatment. 5, 6 Approximately 10-15% of patients presenting with apparent lower GI bleeding actually have a briskly bleeding upper GI source.