What are the differential diagnoses for lower gastrointestinal bleeding?

Differential Diagnoses for Lower Gastrointestinal Bleeding

The most common causes of LGIB are diverticular disease (19-28%), angiodysplasias/vascular malformations, hemorrhoids (28%), colorectal neoplasms (10-11%), colitis (infectious, inflammatory, ischemic), and anorectal disorders, with age being the critical factor in narrowing your differential. 1, 2, 3, 4

Age-Stratified Differential Approach

Patients <50 Years Old

• Anorectal sources predominate 3:
  • Hemorrhoids (most common in this age group)
  • Anal fissures
  • Infectious colitis
  • Inflammatory bowel disease (if systemically unwell)
  • Juvenile polyps (in children/adolescents)

Patients >70 Years Old

• Left colonic sources are most common 3:
  • Diverticular disease (significantly more common with advancing age)
  • Angiodysplasias
  • Colorectal cancer
  • Ischemic colitis

Common Causes Across All Ages

The "big five" account for the vast majority of cases 2, 4:

1. Diverticular disease (19-28% of cases)
2. Angiodysplasias/vascular malformations
3. Hemorrhoids (28% of cases, especially younger patients)
4. Colorectal neoplasms (10-11%): adenomatous polyps, cancer
5. Colitis: infectious, inflammatory bowel disease, ischemic

Additional Important Differentials

• Postpolypectomy bleeding 2
• Anorectal disorders: fissures, proctitis
• Meckel diverticulum (pediatric population) 5
• Radiation proctitis (history-dependent)

Critical Pitfall: Rule Out Upper GI Source First

Up to 11-15% of patients presenting with apparent LGIB actually have an upper GI source 1. Suspect UGIB when you see:

• Brisk rectal bleeding with hemodynamic instability
• Elevated BUN/creatinine ratio
• History of peptic ulcer disease or portal hypertension
• Antiplatelet drug use
• Risk factors for UGIB

In unstable patients with suspected LGIB, perform CTA first (not colonoscopy), as it can identify upper GI, small bowel, or colonic sources without bowel preparation 1. If CTA is negative and patient remains unstable, proceed to upper endoscopy before colonoscopy.

Rare but Important Causes

• Appendiceal hemorrhage (obscure but documented) 6
• Small bowel sources (distinct entity, requires capsule endoscopy if other investigations negative) 1
• Henoch-Schönlein purpura, hemolytic uremic syndrome (pediatric, systemically unwell) 5

Clinical Context Modifiers

In pregnancy: Most commonly hemorrhoids and anal fissures, but don't overlook inflammatory bowel disease or malignancy—investigations are safe and should not be withheld 7.

In pediatric patients who appear well: Consider swallowed blood, allergic colitis, anal fissures, lymphonodular hyperplasia 5.

In pediatric patients who appear unwell: Consider necrotizing enterocolitis, volvulus, Hirschsprung disease, intussusception, Meckel diverticulum 5.