What causes rectal bleeding after stool?

Rectal Bleeding After Stool: Common Causes and Diagnostic Approach

Blood appearing after a bowel movement most commonly originates from hemorrhoids, anal fissures, or diverticulosis in adults, though the specific cause varies significantly by age and clinical presentation. 1, 2

Most Common Causes by Age

Adults (Age 63-77 years)

• Diverticulosis is the single most common cause, accounting for 20-41% of acute lower GI bleeding cases, with incidence increasing dramatically with age (>200-fold increase from age 20 to 80) 1, 2
• Hemorrhoids and anal fissures are the most frequent causes of chronic, bright red rectal bleeding, particularly when blood appears on toilet paper or coating the stool 3, 4
• Angiodysplasia accounts for only 2-15% of cases in most studies 1, 2
• Cancer and polyps cause 6-27% of cases, but typically present with chronic intermittent bleeding rather than acute hemorrhage 1, 2

Younger Adults (Under 55 years)

• Hemorrhoids account for 96% of identifiable anal causes in patients with chronic bright red bleeding 4
• Anal fissures represent 4% of cases 4
• Colorectal neoplasia is found in only 6% of low-risk patients under 55 with an identifiable anal source 4

Critical Initial Assessment

Determine Bleeding Severity

• Hemodynamic stability must be assessed immediately - check blood pressure, heart rate, and signs of shock 1
• Approximately 80-85% of lower GI bleeding stops spontaneously, but 50% of diverticular bleeding cases require transfusion 2
• Mortality rate is 2-4% for acute lower GI bleeding 1, 2

Exclude Upper GI Source

• 10-15% of patients with severe bright red rectal bleeding actually have an upper GI source - this must be ruled out first, especially with massive bleeding 1, 2
• Consider nasogastric tube placement and upper endoscopy if hematemesis, melena, or hemodynamic instability is present 1

Diagnostic Algorithm

For Chronic, Bright Red Bleeding (Stable Patients)

1. Digital rectal examination to identify fissures, masses, or hemorrhoids 3
2. Rigid or flexible sigmoidoscopy as initial endoscopic evaluation 4, 5
3. Colonoscopy if no source identified or if patient has risk factors:
   • Age >55 years 4
   • Family history of colorectal cancer 4
   • Altered bowel habits or abdominal pain 4
   • No identifiable anal source 4

For Acute, Severe Bleeding (Unstable Patients)

1. Resuscitation first - IV fluids, blood products to maintain hemoglobin >7 g/dL (>9 g/dL if massive bleeding or cardiovascular disease) 1
2. Upper endoscopy to exclude upper GI source if severe hematochezia 1
3. CT angiography before colonoscopy in hemodynamically unstable patients with very heavy bleeding to rapidly localize the source 2
4. Colonoscopy after stabilization and bowel preparation when feasible 1, 5
5. Angiography with embolization if bleeding persists and CT angiography shows active extravasation (requires bleeding rate >0.5 mL/min) 1

Specific Clinical Scenarios

Inflammatory Bowel Disease

• Rectal bleeding occurs in 45% of Crohn's colitis cases (32% overt, 11% occult) 6
• Bleeding is 10 times more frequent in Crohn's colitis than in small bowel Crohn's disease 6
• 86% of patients with Crohn's colitis and rectal involvement have bleeding 6
• Medical management is first-line; surgery reserved for massive, uncontrollable hemorrhage 6

Post-Radiation Bleeding

• Do not biopsy radiation-induced telangiectasia due to risk of fistula formation or necrosis 1
• Optimize stool consistency and reduce anticoagulants if possible 1
• Definitive treatment options include hyperbaric oxygen therapy, argon plasma coagulation, or formalin therapy 1
• Bleeding typically recurs when treatment is stopped 1

Common Pitfalls to Avoid

• Never assume hemorrhoids without proper evaluation - symptoms attributed to hemorrhoids frequently represent other pathology 7
• Do not rely on sigmoidoscopy alone - it misses more than one-fifth of polyps 7
• Patient descriptions of bleeding are unreliable - physician-documented bleeding has a 22.5% diagnostic yield versus 5.9% for patient-reported bleeding only 5
• Biopsy irradiated mucosa cautiously - carries significant risk of complications 1
• Consider all age-appropriate differential diagnoses - in children, food protein-induced enterocolitis syndrome can present with rectal bleeding 7

When to Refer for Urgent Evaluation

• Hemodynamic instability or signs of shock 1
• Massive bleeding requiring transfusion 1, 2
• Age >55 years with new-onset bleeding 4
• Associated symptoms: weight loss, altered bowel habits, abdominal pain, fever 7, 4
• Family history of colorectal cancer or inflammatory bowel disease 4
• No identifiable anal source on initial examination 4, 5

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