Guide — Gastrointestinal
Lower GI Bleeding
Lower GI bleeding (LGIB) originates distal to the ligament of Treitz — small bowel, colon, rectum, or anus. It most commonly presents as hematochezia and is the leading cause of GI bleeding in adults over 50.
11 min read · Gastrointestinal
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Common Causes
| Cause | Key Features |
|---|---|
| Diverticulosis | Most common cause in adults >50. Outpouchings of colonic wall. Painless, large-volume bleeding. Usually stops spontaneously. |
| Colorectal cancer | Occult or bright red blood. Associated with weight loss, change in bowel habits, iron deficiency anemia. Risk increases >50 years. |
| Angiodysplasia | Vascular malformations in colon. Associated with older adults, aortic stenosis, von Willebrand disease. Recurrent intermittent bleeding. |
| Inflammatory bowel disease (IBD) | Crohn's disease or ulcerative colitis. Associated with diarrhea, cramping, mucus in stool, systemic symptoms. |
| Ischemic colitis | Reduced blood flow to colon (splenic flexure most vulnerable). Presents with sudden crampy pain then hematochezia. Common in elderly. |
| Hemorrhoids | Most common cause of rectal bleeding overall. Bright red blood on toilet paper or in bowl. Usually non-massive. Internal hemorrhoids are painless. |
| Anal fissure | Tear in anal canal. Painful bright red bleeding with defecation. Associated with constipation and low-fiber diet. |
| Polyps | Precancerous lesions. May cause occult or minor bleeding. Detected and removed at colonoscopy. |
Hematochezia
Hematochezia — bright red or maroon blood per rectum — is the hallmark presentation of lower GI bleeding. The color and character of rectal bleeding provides important clues to the source.
| Blood Appearance | Likely Source | Examples |
|---|---|---|
| Bright red blood on toilet paper | Anorectal (most distal) | Hemorrhoids, anal fissure |
| Bright red blood in toilet bowl | Rectum or distal colon | Internal hemorrhoids, rectal cancer, polyp |
| Bright red blood mixed with stool | Sigmoid or descending colon | Diverticulosis, IBD, angiodysplasia |
| Maroon-colored stool | Right colon or small bowel | Cecal diverticulosis, angiodysplasia, Meckel's diverticulum |
| Blood + mucus | Inflammatory process | IBD, infectious colitis, colorectal cancer |
| Melena (black tarry) | Upper GI (or right colon) | PUD, esophageal varices — rule out upper GI source first |
Assessment Findings
Hemodynamic stability is the top priority. Most LGIB patients are more stable than UGIB patients — but large-volume diverticular or angiodysplastic bleeds can be life-threatening.
Vital Signs
- ✦Tachycardia is first sign of volume loss
- ✦Hypotension = massive hemorrhage
- ✦Orthostatic hypotension = significant blood loss
- ✦Fever suggests inflammatory or infectious etiology
GI History
- ✦Bowel habit changes (cancer)
- ✦Pain + diarrhea (IBD)
- ✦Painless bleeding (diverticulosis, hemorrhoids)
- ✦Tenesmus — rectal irritation, IBD, cancer
Associated Symptoms
- ✦Unintentional weight loss (cancer)
- ✦Abdominal cramping before hematochezia (ischemic colitis)
- ✦Anal pain with defecation (anal fissure)
- ✦Family history of colon cancer or polyps
Laboratory
- ✦CBC: hemoglobin, hematocrit (may lag 6–24 hrs)
- ✦BMP: renal function, electrolytes
- ✦Coagulation studies: PT/INR, aPTT (bleeding risk)
- ✦BUN normal or low (vs elevated in UGIB)
Diagnostic Workup
| Test | Purpose | Priority |
|---|---|---|
| Upper endoscopy (EGD) first | Rule out massive UGIB presenting as hematochezia | First if hemodynamically unstable or UGIB suspected |
| Colonoscopy | Gold standard for LGIB — identifies source in 70–90% of cases, allows therapeutic intervention | Urgent (within 24 hrs) for active or significant bleed |
| CT angiography (CTA) | Detects active bleeding ≥0.3 mL/min. Non-invasive. Guides IR embolization. | For active, rapid hemorrhage — can precede colonoscopy |
| Tagged RBC scan (nuclear medicine) | Detects active bleeding ≥0.1 mL/min. Less specific than CTA. | When CTA negative but bleeding suspected |
| Capsule endoscopy | Small bowel evaluation (Crohn's, obscure bleeding) | After negative upper and lower endoscopy |
| Anoscopy/proctoscopy | Direct visualization of anorectal area | For isolated anorectal bleeding (hemorrhoids, fissure) |
Treatment Overview
Hemodynamic resuscitation
Two large-bore IVs. IV fluid resuscitation. Transfuse pRBCs for Hgb <7 (or <8 in cardiac disease). Correct coagulopathy with FFP, platelets, vitamin K as indicated. Activate massive transfusion protocol if massive hemorrhage.
Rule out upper GI source
Place NGT — if bilious return (no blood), upper GI source less likely. If clinical suspicion for UGIB, perform EGD first before colonoscopy. BUN elevation suggests upper GI source. NG lavage is controversial but sometimes used.
Endoscopic management
Colonoscopy: hemostasis via epinephrine injection, thermal coagulation, clips, or banding for bleeding lesion. Most effective when performed urgently after adequate bowel prep. Polyp removal (polypectomy) for bleeding polyps.
Angiographic embolization (Interventional Radiology)
For active bleeding not amenable to endoscopic control. CTA or tagged RBC scan guides catheter placement. Super-selective embolization reduces ischemia risk. Success rate 85–90% for acute diverticular bleed.
Surgery
Reserved for refractory bleeding (failed endoscopic and IR therapy), hemodynamic instability requiring massive transfusion, or known cancer requiring resection. Segmental colectomy preferred over subtotal colectomy when source localized.
Nursing Priorities
Assess hemodynamic stability — vitals every 15 minutes
Tachycardia is the earliest sign of significant blood loss. Orthostatic hypotension (drop ≥20 mmHg sitting to standing) indicates ≥500 mL volume loss. Notify provider for any hemodynamic change.
Establish IV access and draw labs
Two large-bore peripheral IVs. CBC, BMP, coagulation panel, type & screen. Communicate blood type and crossmatch status with blood bank. Anticipate transfusion.
Accurate characterization and documentation of bleeding
Document appearance, amount, and frequency of rectal bleeding. Save specimens if possible. Accurate description guides diagnosis: bright red vs maroon vs tarry vs occult.
NPO status and bowel prep preparation
NPO for colonoscopy. Colonoscopy bowel prep may be ordered urgently — administer as directed. Coordinate timing with GI procedure team.
Monitor for colon ischemia signs
Sudden severe crampy abdominal pain followed by hematochezia in elderly patients = ischemic colitis. Notify provider immediately — requires urgent imaging.
Patient education on colon cancer screening
If bleeding is from polyps or cancer, educate on screening recommendations. First-degree relative with colon cancer = screening starts at 40 or 10 years before their diagnosis age.
NCLEX Pearls
- ✦Lower GI bleeding = source distal to ligament of Treitz. Most common causes: diverticulosis (#1 in adults >50), colorectal cancer, angiodysplasia.
- ✦Hematochezia (bright red blood per rectum) = typical lower GI bleed. But massive UGIB can also present as hematochezia (rapid transit).
- ✦Key differentiator: BUN — elevated BUN:Cr ratio suggests upper GI bleed (blood digested as protein). Normal BUN = lower GI source more likely.
- ✦Diverticular bleed is usually painless — if pain is present, consider diverticulitis, ischemic colitis, or IBD instead.
- ✦Painless rectal bleeding on toilet paper in young adults = most likely hemorrhoids — but colon cancer must be ruled out in older adults.
- ✦Ischemic colitis: sudden crampy pain then bright red blood in elderly or post-vascular surgery patients — urgent CT scan.
- ✦First assessment priority: hemodynamic stability — not identifying the exact source. Stabilize first, then diagnose.
- ✦Colonoscopy is the gold standard for LGIB diagnosis AND treatment — can identify and treat bleeding lesion in one procedure.
- ✦Colorectal cancer screening: standard colonoscopy at age 45 (USPSTF). Positive FIT/FOBT = diagnostic colonoscopy within 6 months.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with American College of Gastroenterology (ACG) / AGA · ASPEN (nutrition support). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →