Undifferentiated lower gastrointestinal bleeding


Gasterointestinal anatomy.
Layers of the Alimentary Canal. The wall of the alimentary canal has four basic tissue layers: the mucosa, submucosa, muscularis, and serosa.
  • Loss of blood from the gastrointestinal tract distal to the ligament of Treitz
    • Majority of cases originate distally to ileocecal valve, rather than small intestines[1]
  • Diverticulosis cause majority, other conditions include colitis, polyps, colorectal cancer, hemorrhoids, anal fissures, inflammatory bowel disease
    • Consider recent procedures such as abdominal surgeries or colonoscopies/polypectomies
    • Must consider upper GI bleed (especially rapid transit) as a source, as a significant number of lower GI bleeds have a concurrent upper GI bleed, brisk or not[2]
  • Cause of bleeding found in <50% of cases[citation needed]
  • 80% of lower GI bleeding will resolve spontaneously[3]

Medication Risk Factors

Clinical Features

Type of blood

  • Hematochezia
    • Usually represents lower GI bleeding
    • Left colonic bleeding tends to be bright red, whereas right colonic is usually maroon and mixed with stool[4]
    • 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 or slow stool transit from lower GI source

Differential Diagnosis

Undifferentiated lower gastrointestinal bleeding


Fecal Occult Blood Test showing positive (A) and positive control (B).
  • Digital rectal exam for guaiac or assessment of anorectal structural abnormalities
  • Consider chart review to search for prior colonoscopy/endoscopy results


  • CBC
    • Consider q3-12hr serial Hgb, depending on suspected severity of bleed
    • Initial Hgb may be normal if bleeding is acute
  • CMP
    • BUN may be elevated if bleeding occurs from site high in GI tract, due to heme digestion to nitrogenous substances reflected in BUN[5]
  • Coags
  • Type and screen/cross
  • 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)


  • NPO, if there is foreseeable endoscopy or surgery
  • Fluid resuscitation for all

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

  • Unstable
    • CT angiography is preferred for hemodynamically unstable patients due to speed[6]
    • 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.
      • Base decision to transfuse on individual clinical factors. Active bleeding and tachycardia may call for transfusion despite normal Hgb
    • Consider withholding and DOACs; consult with a specialist or the physician who prescribed the medication especially if high-risk cardiac pathology is present
    • Consult GI for emergent sigmoidoscopy/colonoscopy (next 24 hours); upper endoscopy may be needed if CTA does not reveal source of GI bleeding
    • Consult interventional radiology for embolization if an extravasating lesion is identified on CTA[7]
    • Consult surgery if endoscopy fails or not available
  • Stable

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[8]
    • Non-actionable unless abdominal pain present



  • Oakland score can help determine if outpatient management is feasible[9]
  • 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. Farrell JJ, Friedman LS. Review article: the management of lower gastrointestinal bleeding. Aliment Pharmacol Ther. 2005 Jun 1;21(11):1281-98. doi: 10.1111/j.1365-2036.2005.02485.x. PMID: 15932359.
  2. Amin SK, Antunes C. Lower Gastrointestinal Bleeding. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK448126
  3. Farrell JJ, Friedman LS. Review article: the management of lower gastrointestinal bleeding. Aliment Pharmacol Ther. 2005 Jun 1;21(11):1281-98. doi: 10.1111/j.1365-2036.2005.02485.x. PMID: 15932359.
  4. Frost J, Sheldon F, Kurup A, Disney BR, Latif S, Ishaq S. An approach to acute lower gastrointestinal bleeding. Frontline Gastroenterol. 2017 Jul;8(3):174-182. doi: 10.1136/flgastro-2015-100606. Epub 2015 Jun 29. PMID: 28839906; PMCID: PMC5558275.
  5. Patel, Sneha MD; Peraza, Jellyana MD; Hasani, Aliaskar MD; Luther, Sanjana MD; Chugh, Rishika MD; Tokayer, Aaron MD, FACG. 611 Finding the Ideal BUN to Creatinine Ratio in an Upper GI Bleed. The American Journal of Gastroenterology 114():p S355, October 2019. | DOI: 10.14309/01.ajg.0000591980.77707.20
  6. 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.
  7. Sengupta, Neil, Feuerstein, Joseph, Jairath, Vipul, et al. Management of Patients With Acute Lower Gastrointestinal Bleeding: An Updated ACG Guideline. Am J Gastroenterol. 2023;118(2):208-231. doi:10.14309/ajg.0000000000002130.
  8. Sullivan SN, Wong C. Runners' diarrhea. Different patterns and associated factors. J Clin Gastroenterol 1992;14:101-104.
  9. Oakland K, Jairath V, Uberoi R, Guy R, Ayaru L, Mortensen N, Murphy MF, Collins GS. Derivation and validation of a novel risk score for safe discharge after acute lower gastrointestinal bleeding: a modelling study. Lancet Gastroenterol Hepatol. 2017 Sep;2(9):635-643. doi: 10.1016/S2468-1253(17)30150-4. Epub 2017 Jun 23. PMID: 28651935.