Lower gastrointestinal bleeding

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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 (see upper GI bleed)
    • 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
  • Consider:
    • ECG (if concern for silent ischemia in patients likely to have CAD)
    • Fibrinogen
    • CTA
    • Tagged red blood cell scan (not typically an emergency study)

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)


Categorize as stable versus unstable using shock index: <1 stable; >1 unstable or suspect active bleeding

  • Unstable
    • Resuscitate, CT angiogram, if CTA does not identify source of bleeding, upper endoscopy if hemodynamic instability [1]
    • Consider transfusing pRBCs/platelets for unstable patients or with very low hemoglobin (<7). with cardiovascular disease use trigger of 8 and target of 10 hemoglobin.
    • Emergent sigmoidoscopy/colonoscopy (next 24 hours)
    • Surgery if endoscopy fails or not available
  • Stable
    • Calculate risk score to determine disposition
      • Oakland score
      • Glasgow-Blatchford score

Major Bleed and Supratherapeutic INR

Special situations

  • Marathon runners - 16% will have hematochezia within 24-48 hrs of race and 85% will be guaiac positive[2]
    • Non-actionable unless abdominal pain present



  • Bleeding from hemorrhoids, anal fissures, or known IBD (hemodynamically stable)
  • No gross blood on rectal exam (hemodynamically stable)
  • Minor, self-terminating bleed with no other indication for admission (shock index >1; low risk score calculated)


  • Melena
  • Significant anemia
  • Hemodynamic instability

See Also

Gastrointestinal Bleeding Pages


  1. Oakland K, Chadwick G, East JE, et al. Diagnosis and management of acute lower gastrointestinal bleeding: guidelines from the British Society of Gastroenterology. Gut 2019;67:776-789.
  2. Sullivan SN, Wong C. Runners' diarrhea. Different patterns and associated factors. J Clin Gastroenterol 1992;14:101-104.