Lower gastrointestinal bleeding

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  • Loss of blood from the gastrointestinal tract distal to the ligament of Treitz
  • Upper GI bleeds are most common source for blood detected in the lower GI system
  • 80% of lower GI bleeding will resolve spontaneouslyScript errorScript error[citation needed]
  • Cause of bleeding found in <50% of casesScript errorScript error[citation needed]
  • Hematochezia unexpectedly originates from upper GI source 10-15% of casesScript errorScript error[citation needed]

Medication Risk Factors

Clinical Features

Type of blood

  • Hematochezia
    • Bright red or maroon-colored bleeding that comes from the rectum
    • Usually represents lower GI bleeding
    • May represent upper GI source if bleeding is brisk
      • Usually accompanied by hematemesis and hemodynamic instability
  • Melena
    • Usually represents bleeding from upper GI source
    • May represent slow bleeding from lower GI source

Differential Diagnosis

Lower gastrointestinal bleeding



  • CBC
  • Chemistries
    • BUN may be elevated if bleeding occurs from site high in GI tract
  • Coags
  • LFTs
  • Type and screen
  • Fibrinogen
  • ECG (if concern for silent ischemia in patients likely to have CAD)
  • CTA
    • Requires brisk bleeding rate (0.5 cc/min) for detectionScript errorScript error[citation needed]
  • Tagged red blood cell scan

Definitive studies

  • Consider:
    • Anoscopy if source of bleeding cannot be identified on external exam
    • Proctoscopy (22cm from anal verge)
    • Sigmoidoscopy (60cm from anal verge)

False Positive Guaiac

  • Red meat
  • Red jello
  • Fruit and vegetables
    • Melon, broccoli, radish, beets
  • Iron (causes GI bleed by irritation)


  • IVF
  • Consider transfusing pRBCs/platelets for unstable patients or with very low hemoglobin (<7)
  • Consider NGT - high possibility for surgery to request
  • Emergent Sigmoidoscopy/colonoscopy (next 24 hours)
  • Surgery if endoscopy fails or not available

Major Bleed and Supratheraputic INR

Special situations

  • Marathon runners - 16% will have hematochezia within 24-48 hrs of race and 85% will be guaiac positive[1]
    • Non-actionable unless abdominal pain present



  • Bleeding from hemorrhoids, anal fissures, or known IBD (hemodynamically stable)
  • No gross blood on rectal exam (hemodynamically stable)


  • Melena
  • Significant anemia
  • Hemodynamic instability

See Also

Upper GI Bleeding


  1. Sullivan SN, Wong C. Runners' diarrhea. Different patterns and associated factors. J Clin Gastroenterol 1992;14:101-104.