Lower GI Bleed — Diagnosis & Management

Key Points

• Treat the circulation first and the anatomic source second.
• Hemodynamically unstable hematochezia may originate from the upper GI tract.
• CT angiography is highly useful for ongoing significant bleeding because it can rapidly localize active extravasation.
• A positive CTA in a patient with brisk bleeding should prompt interventional radiology consideration for embolization.
• Stable patients generally benefit from adequate bowel preparation before colonoscopy rather than an unprepped emergency procedure.
• Do not assume hemorrhoids explain substantial bleeding without appropriate evaluation.
• Routine tranexamic acid is not recommended for GI bleeding.
• Anticoagulant reversal and later resumption must balance bleeding severity against the patient's underlying thrombotic indication.

Algorithm

1. Assess hemodynamics, establish IV access, obtain labs and type/cross, and resuscitate active shock.
2. Consider an upper GI source when hematochezia is accompanied by instability or upper-GI clues.
3. For ongoing hemodynamically significant lower bleeding, obtain CT angiography.
4. If CTA localizes active bleeding, involve interventional radiology for embolization while continuing resuscitation.
5. If bleeding slows or stops, perform bowel preparation and colonoscopy for diagnosis and endoscopic therapy.
6. Use surgery for refractory bleeding, ischemic necrosis, perforation, or lesions not controlled by endoscopy or embolization.
7. Review anticoagulants and antiplatelets and restart them after hemostasis according to thrombotic risk.
8. Arrange definitive follow-up for diverticular disease, neoplasia, inflammatory bowel disease, or another identified cause.

Clinical Synopsis & Reasoning

Assess blood pressure, orthostasis, mental status, skin perfusion, ongoing stool appearance, anticoagulant use, liver disease, and cardiovascular comorbidity. Large-volume red or maroon stool with shock can arise from a proximal source, including upper GI bleeding, so consider nasogastric-free upper-source assessment based on clinical clues and endoscopy when appropriate. Common colonic causes include diverticular hemorrhage, angioectasia, ischemic colitis, hemorrhoids, colorectal neoplasia, inflammatory bowel disease, post-polypectomy bleeding, and radiation injury. Painless large-volume bleeding favors diverticular disease or angioectasia, while abdominal pain and bloody diarrhea raise concern for ischemia or colitis. Obtain CBC, metabolic panel, coagulation studies when relevant, and type and screen or crossmatch. Risk scores can support disposition but do not replace clinician assessment. Digital rectal examination can confirm blood and identify anorectal lesions, but finding hemorrhoids does not exclude a more proximal source. CT angiography requires active bleeding to localize extravasation and is particularly useful when hemorrhage is brisk. Colonoscopy should follow adequate preparation unless ongoing instability requires faster radiologic or angiographic intervention.

Treatment Strategy & Disposition

Resuscitate with IV access and red-cell transfusion using a restrictive approach in most patients, modified for ongoing shock, active coronary ischemia, or other special circumstances. Reverse life-threatening anticoagulant-associated bleeding according to the agent and severity, while avoiding unnecessary reversal in minor bleeding. For ongoing hemodynamically significant hematochezia, obtain CT angiography promptly. A positive study should lead to interventional radiology for transcatheter embolization when feasible, with endoscopy or surgery chosen according to anatomy and local expertise. For patients who stabilize, prepare the colon and perform inpatient colonoscopy on an appropriate nonemergent timeline; rushing unprepped colonoscopy within a few hours has not consistently improved outcomes. Endoscopic hemostasis options include clips, thermal therapy, banding, or combination techniques depending on the lesion. Ischemic colitis requires perfusion optimization and surgical consultation when peritonitis, gangrene, or ongoing deterioration is present. Avoid routine tranexamic acid for GI bleeding because large trials did not show benefit and identified harms. Restart antithrombotic therapy after hemostasis using individualized thrombotic-versus-rebleeding assessment.

Epidemiology / Risk Factors

• Diverticulosis is a common cause of acute lower GI hemorrhage in adults.
• Angioectasia becomes more common with age and comorbidity.
• Ischemic colitis is an important painful bleeding cause, especially in older adults or low-flow states.
• Anticoagulant and antiplatelet use increases bleeding severity and complicates management.
• Many lower GI bleeds stop spontaneously, but recurrent bleeding is common for several etiologies.

Investigations

Imaging/Endoscopy Selection

Pharmacology

Prognosis / Complications

• Most patients stabilize without surgery, particularly when bleeding is diverticular and self-limited.
• Mortality is driven more by age, comorbidity, shock, and transfusion burden than by the colonic lesion alone.
• Rebleeding is common after diverticular hemorrhage and angioectasia.
• Successful arterial embolization can rapidly control ongoing focal bleeding but carries a small ischemia risk.
• Colorectal cancer discovered during bleeding evaluation has prognosis determined by stage and should be linked to definitive oncologic care.

Patient Education / Counseling

• Return urgently for recurrent large-volume red or black stool, fainting, chest pain, dyspnea, or profound weakness.
• Review NSAID use and avoid nonessential agents that increase recurrent bleeding risk.
• Do not stop prescribed anticoagulants or antiplatelets permanently without a clinician-directed plan, because thrombosis risk may exceed rebleeding risk.
• Complete recommended colonoscopy or outpatient evaluation even if bleeding stops, particularly when the source was not definitively identified.
• Discuss iron replacement and follow-up CBC when substantial blood loss caused anemia.

Notes

Lower GI bleeding is increasingly managed by matching the test to the bleeding rate. Brisk ongoing hemorrhage is best localized quickly with CT angiography so interventional radiology can act on a positive result. A patient who stabilizes benefits from a properly prepared colonoscopy rather than a rushed, poorly visualized examination. Throughout the pathway, the clinician must remember that hematochezia can be upper GI bleeding, that antithrombotic decisions have competing risks, and that stopping the bleeding is only the first step when the underlying lesion requires definitive follow-up.

References

1. ACG Guideline: Management of Patients With Acute Lower Gastrointestinal Bleeding — Link