Summary

Acute lower gastrointestinal bleeding is a medical emergency where bleeding occurs from the small intestine (distal to ligament of Treitz), colon, rectum, or anus. Unlike upper GI bleeding where blood is digested (turning stools black), lower GI bleeding presents as bright red or maroon blood (hematochezia) because it hasn't been digested. Picture your lower digestive tract as a series of pipes—when one springs a leak, fresh blood appears in your stools. This condition affects approximately 20-30 per 100,000 people annually and carries a mortality of 2-4% overall, rising to 10-15% in high-risk patients. The key to management is rapid assessment, resuscitation if needed, risk stratification, and appropriate investigation (colonoscopy, CT angiography, or nuclear medicine scans) to identify and treat the bleeding source. Most bleeds stop spontaneously, but those that don't require endoscopic, radiological, or surgical intervention.

Key Facts

• Definition: Bleeding from GI tract distal to ligament of Treitz (jejunum, ileum, colon, rectum, anus)
• Incidence: 20-30 per 100,000/year; ~20,000-30,000 hospitalizations/year (UK)
• Mortality: 2-4% overall; 10-15% in high-risk patients
• Time to investigation: Urgent (<24h) for high-risk, routine for low-risk
• Critical threshold: Hemoglobin drop >2g/dL or need for >2 units blood
• Key investigation: Colonoscopy (first-line), CT angiography (if active bleeding), nuclear medicine scan (if intermittent)
• First-line treatment: IV access, fluid resuscitation, blood transfusion if needed, urgent colonoscopy

Clinical Pearls

"Hematochezia = Lower GI bleed (usually)" — Bright red or maroon blood per rectum usually indicates lower GI bleeding. However, massive upper GI bleeding can also cause hematochezia if blood passes through quickly. Always consider upper GI source if hemodynamically unstable.

"Most diverticular bleeds stop spontaneously" — 80% of diverticular bleeds stop on their own. The challenge is identifying the 20% that don't and treating them before they cause significant blood loss.

"Colonoscopy is first-line investigation" — Colonoscopy can both diagnose and treat most lower GI bleeds. CT angiography is useful if bleeding is too active for colonoscopy or if colonoscopy is negative.

"Angiodysplasia is common in elderly" — In patients over 65 with lower GI bleeding, angiodysplasia (abnormal blood vessels) is a common cause, especially if no diverticula seen.

Why This Matters Clinically

Acute lower GI bleeding is a common emergency that can cause significant blood loss. While mortality is lower than upper GI bleeding, rapid blood loss can still lead to hypovolaemic shock and death. The key is early recognition, appropriate resuscitation, and timely investigation to identify and treat the bleeding source. Delayed recognition or inappropriate management can lead to complications. Protocol-driven management focusing on resuscitation, risk assessment, and appropriate investigation can reduce mortality and morbidity.

Structured Approach: ABCDE

A - Airway

• Assessment: Usually patent
• Action: Secure if compromised

B - Breathing

• Look: Respiratory rate, use of accessory muscles
• Listen: Usually normal (unless severe anemia)
• Measure: SpO2 (usually normal unless severe)
• Action: Oxygen if hypoxic or severe anemia

C - Circulation

• Look: Skin colour (pale), capillary refill
• Feel: Pulse (rate, volume), BP (lying and standing)
• Listen: Heart sounds (tachycardia)
• Measure: BP (both arms), HR, ECG
• Action: IV access x2 (large bore), fluid resuscitation

D - Disability

• Assessment: GCS, mental status
• Finding: May be confused if hypovolaemic
• Action: Check glucose; consider if hypovolaemia causing confusion

E - Exposure

• Look: Full body examination, look for stigmata of liver disease
• Feel: Abdomen (tenderness, masses)
• Action: PR examination (essential - check for blood, masses)

Specific Examination Findings

Cardiovascular Assessment:

Postural Blood Pressure:

• Technique: Measure BP lying, then standing
• Finding: Drop >20mmHg systolic = significant volume loss
• Significance: Indicates need for fluid resuscitation

Pulse Assessment:

• Rate: Tachycardia (compensatory)
• Volume: Weak if significant blood loss
• Rhythm: Usually regular

Abdominal Examination:

• Inspection: Distension, scars, visible masses
• Palpation: Tenderness (colitis, ischemia), masses (tumors)
• Auscultation: Bowel sounds (usually normal, may be hyperactive if colitis)

Rectal Examination (Essential):

• Purpose: Confirm bleeding, assess for masses, check anal canal
• Finding:
  • Blood: Bright red, maroon, or mixed
  • Masses: Tumors, hemorrhoids
  • Tenderness: Fissures, proctitis
• Note: Always do PR in GI bleeding

Special Tests

Natural History (Without Treatment)

Untreated Lower GI Bleeding:

• Mortality: 10-15% if massive, untreated
• Progression: Continued bleeding → hypovolaemic shock → death
• Time course: Death within hours if massive bleeding untreated

Outcomes with Treatment

Factors Affecting Outcomes:

Good Prognosis:

• Low risk (stable, small volume)
• Diverticular bleeding (usually stops spontaneously)
• Anorectal cause (hemorrhoids, fissures)
• Young, healthy patient
• No comorbidities
• Successful endoscopic therapy

Poor Prognosis:

• High risk (unstable, massive bleeding)
• Tumor (bleeding from malignancy)
• Elderly, multiple comorbidities
• Failed endoscopic therapy
• Rebleeding
• Need for surgery

Prognostic Factors

Key Guidelines

1. NICE Guidelines (2012) — UK guidelines for acute lower GI bleeding. National Institute for Health and Care Excellence

Key Recommendations:

• Risk stratify clinically
• Urgent colonoscopy for high-risk (<24h)
• Endoscopic therapy for active bleeding
• Evidence Level: 1A

2. American College of Gastroenterology Guidelines (2016) — US guidelines for lower GI bleeding. American College of Gastroenterology

Key Recommendations:

• Colonoscopy first-line investigation
• CT angiography if too active for colonoscopy
• Endoscopic therapy for high-risk stigmata
• Evidence Level: 1A

Landmark Trials

Strate et al. (2005) — Early Colonoscopy in Lower GI Bleeding

• Patients: 100 patients with lower GI bleeding
• Intervention: Early colonoscopy (<24h) vs. delayed
• Key Finding: Early colonoscopy identified more bleeding sources
• Clinical Impact: Established early colonoscopy as standard
• PMID: 15758907

Evidence Strength

What is Acute Lower GI Bleeding?

Imagine your digestive system as a series of tubes. In acute lower GI bleeding, one of the lower parts (your small intestine, colon, or rectum) starts bleeding. You'll see bright red or maroon blood when you go to the toilet—either mixed with your stool or coming out on its own. This happens when something damages the lining of your lower digestive tract—like small pouches (diverticula), abnormal blood vessels (angiodysplasia), inflammation (colitis), or sometimes tumors.

In simple terms: You're bleeding from your lower intestine or colon, and fresh blood appears in your stools or when you go to the toilet.

Why does it matter?

Acute lower GI bleeding can be serious because you can lose a lot of blood. Your body needs blood to carry oxygen to your organs—without enough blood, your organs can start to fail. Even with the best treatment, about 2-4 out of 100 people don't survive, and this rises to 10-15 out of 100 in people who are already unwell. The good news? Most bleeds stop on their own, and with quick treatment (fluids, blood transfusion if needed, and a camera test to find and treat the cause), most people recover completely.

Think of it like this: It's like a pipe springing a leak—you need to find the leak and fix it before too much water (blood) is lost.

How is it treated?

1. Stopping the Bleeding: Doctors give you fluids and sometimes blood through a drip to replace what you've lost and keep your blood pressure up.

2. Finding the Cause: Doctors do a test called a colonoscopy—a thin, flexible camera is passed through your bottom into your colon to see where the bleeding is coming from. This is done under sedation so you don't feel it.

3. Treating the Bleeding: If the bleeding is still active or looks likely to bleed again, doctors can treat it through the camera:

• Clips: Small clips to close the bleeding vessel
• Heat treatment: Cautery to seal the bleeding vessel
• Injections: Medicine injected around the bleeding area

4. Other Treatments:

• If bleeding is too active: Doctors may use CT scans to find the bleeding, then block the blood vessel (embolization)
• If other treatments fail: Rarely, surgery may be needed to remove the bleeding part

The goal: Stop the bleeding, find and fix the cause, and prevent it happening again.

What to expect

In the Hospital:

• First few hours: Doctors will act quickly to stabilize you—fluids, blood if needed, and prepare for the camera test
• Day 1: You'll have the colonoscopy (camera test) to find and treat the bleeding
• Days 2-3: You'll be monitored closely to make sure the bleeding doesn't start again
• Days 3-5: If everything is stable, you can usually go home

After Going Home:

• Medications: You may need medicines to help healing
• Diet: Usually a normal diet, but avoid things that irritate your colon
• Follow-up: Doctor visits and sometimes repeat camera tests to make sure everything is healed
• Lifestyle: Stop smoking, avoid NSAIDs (like ibuprofen), reduce alcohol if that was a factor

Recovery Time:

• In hospital: Usually 3-5 days
• At home: Most people feel back to normal within 1-2 weeks
• Full healing: Usually within 4-8 weeks

When to seek help

Call 999 (or your emergency number) immediately if:

• You pass bright red or maroon blood from your bottom
• You feel very weak or faint
• You feel dizzy or lightheaded
• Your heart is racing
• You feel confused or "not yourself"

See your doctor urgently if:

• You've had lower GI bleeding before and it happens again
• You're taking blood thinners and notice blood in your stools
• You have ongoing abdominal pain with bleeding
• You're losing weight unexpectedly

Remember: If you pass blood from your bottom, especially if it's a lot or you feel unwell, don't wait—get emergency help immediately. This can be serious and needs prompt treatment.

Conditions to Consider

Acute lower GI bleeding must be distinguished from other causes of rectal bleeding and from upper GI bleeding presenting with hematochezia:

Upper GI Bleeding Presenting as Hematochezia

Clinical Scenario:

• Massive upper GI bleeding can present with bright red blood per rectum (hematochezia) because blood transits so quickly through the GI tract
• Clue: Usually hemodynamically unstable, may have history of PUD, liver disease, varices
• Investigation: Upper endoscopy first if suspected (don't assume lower GI just because bright red blood)
• Management: Treat as upper GI bleeding (PPI, endoscopic therapy, blood transfusion)

When to Suspect:

• Very rapid bleeding with hemodynamic instability
• History of liver disease, PUD, varices
• Elevated urea:creatinine ratio (blood absorbed from upper GI tract)
• Nasogastric aspirate shows blood (although absence doesn't exclude it)

Differentiating Key Causes

1. Diverticular vs. Angiodysplasia:

2. Ischemic vs. IBD Colitis:

3. Benign vs. Malignant Bleeding:

"Can't Miss" Diagnoses

1. Massive Upper GI Bleeding (Presenting as Hematochezia):

• Clue: Hemodynamic instability, very rapid bleeding, elevated urea:creatinine
• Key: Don't assume lower GI just because bright red blood
• Investigation: Upper endoscopy if suspected
• Management: Treat as upper GI bleeding

2. Colorectal Cancer:

• Clue: Weight loss, change in bowel habit, chronic anemia
• Key: Colonoscopy with biopsy mandatory in all cases
• Investigation: Colonoscopy, CT staging if cancer confirmed
• Management: Surgical resection

3. Ischemic Colitis:

• Clue: Sudden onset, severe pain, vascular risk factors
• Key: Can progress to infarction and perforation
• Investigation: Colonoscopy (shows segmental ischemia), CT (shows bowel wall thickening)
• Management: Conservative if not transmural, surgery if perforation/infarction

4. Inflammatory Bowel Disease (Severe Flare):

• Clue: Diarrhea, abdominal pain, systemic symptoms (fever, weight loss)
• Key: Can cause toxic megacolon if severe
• Investigation: Colonoscopy with biopsy
• Management: Steroids, immunosuppression, may need surgery if toxic megacolon

Primary Prevention

Primary prevention focuses on reducing the risk of developing lower GI bleeding in at-risk populations:

Dietary Measures:

• High-fiber diet: Reduces constipation, may reduce diverticular complications
• Adequate hydration: Prevents constipation
• Avoid constipation: Reduces hemorrhoidal bleeding

Medication Review:

• NSAIDs: Stop if possible, use lowest dose for shortest time
• Anticoagulants: Use only if indicated, monitor INR/anticoagulation levels
• Antiplatelets: Use only if indicated (cardiovascular disease, stroke prevention)

Secondary Prevention (Preventing Rebleeding)

For patients who have had one episode of lower GI bleeding:

1. Treat Underlying Cause:

2. Medication Optimization:

Anticoagulation/Antiplatelet Review:

• Balance bleeding vs. thrombosis risk:
  • Continue if high thrombotic risk (mechanical valve, AF with CHA2DS2-VASc ≥2, recent VTE)
  • Stop temporarily if low thrombotic risk (primary prevention, low-risk AF)
  • Resume after bleeding controlled (usually within 7-14 days)

3. Surveillance Colonoscopy:

For patients at high risk of recurrence:

Tertiary Prevention (Managing Recurrent Bleeding)

For patients with recurrent bleeding despite optimal management:

1. Angiodysplasia (Recurrent):

• Medical therapy:
  • Estrogen-progesterone: May reduce bleeding frequency
  • Octreotide: May reduce bleeding in selected cases
  • Tranexamic acid: Antifibrinolytic, may reduce bleeding
• Repeat endoscopic therapy: Cautery or argon plasma coagulation
• Surgery: If medical/endoscopic therapy fails (rare)

2. Diverticular Bleeding (Recurrent):

• Elective colectomy: Consider if >2 episodes requiring transfusion
• Segmental resection: If bleeding site identified
• Risk-benefit: Balance surgery risk vs. bleeding risk

3. IBD (Recurrent Flares with Bleeding):

• Optimize medical therapy: Biologics, immunosuppression
• Surgery: Colectomy if medically refractory
• Monitor closely: Regular surveillance

4. General Measures:

• Iron supplementation: For chronic anemia
• Avoid triggers: NSAIDs, excessive alcohol
• Patient education: Warning signs, when to seek help

Specific Clinical Scenarios

Elderly on Anticoagulation:

• Challenge: High bleeding risk vs. high thrombotic risk
• Strategy:
  • Optimize anticoagulation (target INR 2-2.5 if warfarin, lower dose DOAC if appropriate)
  • PPI co-prescription for upper GI protection
  • Regular review of indication for anticoagulation
  • Patient education on warning signs

Patients with Diverticulosis (Asymptomatic):

• No need for treatment: Asymptomatic diverticulosis doesn't need treatment
• High-fiber diet: May reduce risk of complications
• Avoid NSAIDs: Increases bleeding risk

Patients Post-Polypectomy:

• Risk of post-polypectomy bleeding: 0.3-6% depending on polyp size
• Prevention:
  • Hold anticoagulation/antiplatelet agents pre-procedure (if safe)
  • Endoscopic clips for high-risk polyps
  • Resume anticoagulation cautiously post-procedure
• Management if bleeding: Repeat colonoscopy, endoscopic therapy

Elderly Patients (>75 years)

Specific Considerations:

• Higher mortality: 10-15% vs. 2-4% in younger patients
• More comorbidities: Cardiovascular disease, renal impairment
• Polypharmacy: Multiple medications increasing bleeding risk

Management Adjustments:

Common Causes in Elderly:

• Angiodysplasia: Most common in >75 years
• Diverticular bleeding: Common in Western elderly
• Ischemic colitis: Vascular disease common

Key Challenges:

• Frailty: May not tolerate aggressive intervention
• Goals of care: May need palliative approach if very frail
• Medication review: Optimize, stop unnecessary drugs

Patients on Anticoagulation

Critical Decision: Stop or Continue?

High Thrombotic Risk (Continue Anticoagulation if Possible):

• Mechanical heart valve (especially mitral)
• Atrial fibrillation with CHA2DS2-VASc ≥4
• Recent VTE (less than 3 months)
• Recent stroke/TIA (less than 3 months)

Lower Thrombotic Risk (Consider Stopping Temporarily):

• Atrial fibrillation with CHA2DS2-VASc less than 2 (primary prevention)
• Remote VTE (>6 months)

Anticoagulation Management by Agent:

When to Resume Anticoagulation:

• General rule: 7-14 days after bleeding controlled
• High thrombotic risk: Earlier (3-7 days)
• Low thrombotic risk: Later (14-30 days) or consider not resuming
• Discuss with cardiology/hematology: Individualize decision

Bridging Anticoagulation:

• Generally not recommended in lower GI bleeding
• Exception: Mechanical mitral valve (consider heparin bridging after bleeding controlled)

Patients with Inflammatory Bowel Disease

Specific Considerations:

• Bleeding may indicate disease flare: Not always diverticula or angiodysplasia
• Immunosuppression complicates management: Risk of infection
• Chronic inflammation increases bleeding risk

Approach to IBD Patient with Acute Bleeding:

1. Assess Disease Activity:

• Ulcerative colitis: Truelove & Witts criteria (severe if >6 bloody stools/day, fever, tachycardia, anemia)
• Crohn's disease: Harvey-Bradshaw Index (assess abdominal pain, diarrhea, systemic symptoms)

2. Investigation:

• Colonoscopy: Assess extent and severity
• Biopsy: Confirm IBD vs. other causes
• Stool culture: Exclude infection (C. diff, CMV)

3. Management:

4. Complications to Watch:

• Toxic megacolon: Colon diameter >6cm, systemically unwell, risk of perforation
• Perforation: Acute abdomen, requires emergency surgery
• Massive bleeding: May need embolization or surgery

5. Long-term Management:

• Optimize medical therapy: Biologics, immunosuppression
• Regular surveillance: Colonoscopy every 1-2 years
• Colorectal cancer screening: IBD increases risk

Patients with Chronic Kidney Disease

Specific Considerations:

• Uremia increases bleeding risk: Platelet dysfunction
• Anemia common: Lower baseline hemoglobin
• Fluid balance critical: Risk of overload

Management Adjustments:

Uremic Bleeding:

• Mechanism: Platelet dysfunction from uremia
• Treatment:
  • Dialysis: Corrects uremia, improves platelet function
  • DDAVP (desmopressin): Improves platelet function temporarily
  • Tranexamic acid: Antifibrinolytic
  • Platelet transfusion: Usually ineffective in uremia

Patients with Liver Disease/Cirrhosis

Specific Considerations:

• Portal hypertension: May cause rectal varices (rare)
• Coagulopathy: Prolonged PT/INR, low platelets
• Higher mortality: Decompensated cirrhosis has poor outcomes

Approach:

1. Exclude Variceal Bleeding:

• Upper endoscopy: Exclude esophageal/gastric varices
• Note: Rectal varices rare but can occur in portal hypertension

2. Correct Coagulopathy (If Possible):

• Vitamin K: If INR elevated and vitamin K deficient
• FFP: If major bleeding and very high INR (>5)
• Platelets: If less than 50 and major bleeding
• Note: Don't over-correct; coagulopathy in cirrhosis is balanced (low pro-coagulants but also low anti-coagulants)

3. Endoscopy:

• Timing: May be higher risk in cirrhosis (sedation, procedure)
• Setting: ICU/HDU if Child-Pugh C
• Caution: Risk of hepatic encephalopathy post-procedure

4. Monitor for Decompensation:

• Hepatic encephalopathy: Blood in GI tract can precipitate
• Acute kidney injury: Hepatorenal syndrome risk
• Sepsis: Increased infection risk

Patients Post-Surgery (Recent Abdominal/Pelvic Surgery)

Specific Considerations:

• Anastomotic bleeding: Bleeding from surgical join
• Bowel manipulation: May have ischemia
• Recent polypectomy: Post-polypectomy bleeding

Approach:

Anastomotic Bleeding (Post-Colorectal Surgery):

• Timing: Usually first 7-14 days post-op
• Investigation: Colonoscopy (careful, don't over-insufflate near anastomosis)
• Management: Endoscopic therapy (clips), may need return to theatre

Post-Polypectomy Bleeding:

• Timing: Immediate (during procedure) or delayed (up to 14 days post)
• Risk factors: Large polyp (>2cm), right colon, anticoagulation
• Management: Repeat colonoscopy, endoscopic therapy (clips, cautery)

Radiation Proctitis (Post-Pelvic Radiotherapy):

• Timing: Acute (during treatment) or chronic (months-years later)
• Features: Rectal bleeding, tenesmus, diarrhea
• Investigation: Proctoscopy/sigmoidoscopy (shows friable mucosa, telangiectasia)
• Management: Topical therapies (sucralfate, steroids), argon plasma coagulation for bleeding telangiectasia

Pregnant Patients

Specific Considerations:

• Rare in pregnancy: Lower GI bleeding uncommon
• Causes: Hemorrhoids most common, IBD flare, colitis
• Investigation challenges: Avoid radiation, colonoscopy has risks

Approach:

1. Assessment:

• Obstetric consultation: Assess fetal wellbeing
• Exclude obstetric causes: Antepartum hemorrhage (vaginal bleeding can be confused)

2. Investigation:

• Anoscopy/proctoscopy: Safe, can diagnose hemorrhoids/fissures
• Flexible sigmoidoscopy: Safer than full colonoscopy
• Full colonoscopy: Only if essential (risk of fetal hypoxia)
• Avoid CT: Radiation exposure to fetus

3. Management:

• Conservative: If hemorrhoids/fissures (fiber, fluids, topical therapy)
• Endoscopic therapy: If active bleeding (safe in experienced hands)
• Surgery: Avoid if possible; only if life-threatening

4. IBD in Pregnancy:

• Continue most medications: Sulfasalazine, mesalazine, prednisolone, azathioprine (safe)
• Avoid methotrexate: Teratogenic
• Biologics: Generally safe (continue infliximab, adalimumab)

Last Reviewed: 2025-12-24 | MedVellum Editorial Team

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists. This information is not a substitute for professional medical advice, diagnosis, or treatment.