What are the differential diagnoses and management options for a patient presenting with hematochezia (blood in stool)?

Differential Diagnoses for Blood on Stool Examination

The differential diagnosis for hematochezia depends critically on hemodynamic status, age, and clinical presentation, with the most common causes being hemorrhoids and diverticulosis in adults, but colorectal cancer, inflammatory bowel disease, ischemic colitis, and angiodysplasia must be systematically excluded through risk stratification and appropriate investigation.

Initial Risk Stratification and Hemodynamic Assessment

• Calculate the shock index (heart rate ÷ systolic blood pressure) immediately upon presentation 1, 2
• A shock index >1 indicates hemodynamic instability and mandates urgent CT angiography rather than routine endoscopy 1, 2
• For hemodynamically stable patients, apply the Oakland score (incorporating age, gender, previous lower GI bleeding, digital rectal examination findings, heart rate, systolic blood pressure, and hemoglobin level) 1
  • Oakland score ≤8 points: safe for outpatient investigation 1
  • Oakland score >8 points: requires hospital admission for colonoscopy 1

Major Differential Diagnoses by Category

Anorectal Causes (Most Common in Younger Patients)

• Hemorrhoids (complicated or uncomplicated): Present with bright red blood per rectum, often with acute anal pain in hemorrhoidal crisis 3
• Anal fissures: Cause acute anal pain with bleeding 3
• Anorectal abscesses: May present with anorectal bleeding and acute pain 3
• Digital rectal examination is mandatory to identify these lesions 3, 1

Colonic Causes

• Diverticulosis: Accounts for 17% of severe hematochezia cases 4
• Angiodysplasia/vascular ectasias: Most common colonic source, representing 30% of severe bleeding cases 4
• Colorectal polyps or cancer: Represent 11% of severe hematochezia; must be excluded especially in patients >60 years 3, 4
• Inflammatory bowel disease (IBD): Consider in patients with chronic diarrhea, urgency, abdominal pain, or weight loss; up to 15% of new IBD diagnoses occur in patients >60 years 3
• Ischemic colitis: More likely in elderly patients (>60 years), particularly those with cardiovascular comorbidities or recent hypotension 3
• Segmental colitis associated with diverticulosis: Consider in elderly patients with left-sided segmental colitis and diverticulosis 3

Small Bowel Causes

• Small bowel angiodysplasia: Presumed in 9% of severe hematochezia cases when colonoscopy is negative 4
• Small bowel ulcers or erosions: May be medication-related (NSAIDs) 3

Upper Gastrointestinal Sources

• Upper GI bleeding presenting as hematochezia: Accounts for 11% of apparent lower GI bleeding, particularly in hemodynamically unstable patients 4, 5
• Always consider an upper GI source in patients with hemodynamic instability, even with hematochezia 2, 5

Other Important Considerations

• Radiation enteritis or colitis: In patients with history of pelvic radiation 3
• NSAID-induced pathology: Common in elderly patients 3
• Microscopic colitis: May present with chronic diarrhea and occult bleeding 3
• Rectal prolapse with strangulation: Rare but life-threatening; presents with irreducible rectal mass and bleeding 3
• Anorectal varices: In patients with portal hypertension or liver disease 3

Diagnostic Algorithm Based on Hemodynamic Status

For Hemodynamically Unstable Patients (Shock Index >1)

1. Perform CT angiography immediately as the first diagnostic step to rapidly localize bleeding 1, 2, 5
   • CTA has 79-95% sensitivity and 95-100% specificity 5
   • Provides fastest, least invasive means to localize bleeding 1
2. Following positive CTA, proceed to catheter angiography with embolization within 60 minutes in centers with 24/7 interventional radiology 1, 2
3. If CTA is negative, perform upper endoscopy immediately to exclude upper GI source 5
4. Colonoscopy is explicitly contraindicated as initial approach when shock index >1 or patient remains unstable after resuscitation 1
5. Surgery is reserved only after failure of angiographic intervention or continued deterioration despite all localization attempts 1

For Hemodynamically Stable Patients

1. Perform digital rectal examination to confirm blood in stool and exclude anorectal pathology 1, 3
2. Obtain complete blood count, serum electrolytes, BUN, creatinine, coagulation assessment, and inflammatory markers (C-reactive protein) 3
3. Blood typing and cross-matching for patients with signs of severe bleeding 3
4. Stool testing for Clostridium difficile in all new presentations of diarrhea, regardless of antibiotic history 3
5. Fecal calprotectin or lactoferrin may help prioritize patients with low probability of IBD for endoscopic evaluation 3
6. Colonoscopy after adequate bowel preparation is the primary diagnostic modality for stable patients 3, 1
   • No evidence that urgent colonoscopy (<24 hours) improves outcomes compared to elective timing (36-60 hours) 5
7. Consider sigmoidoscopy and esophagogastroduodenoscopy in IBD patients with gastrointestinal bleeding 3

Age-Specific Considerations

Patients <50 Years

• Anorectal causes (hemorrhoids, fissures) are most common 6
• However, colorectal cancer cannot be excluded based on age alone 6
• Clinical presentation alone has limited value in determining need for investigation 6

Patients ≥60 Years

• Higher likelihood of serious pathology: colorectal cancer, ischemic colitis, diverticulosis, angiodysplasia 3
• Vigorous diagnostic approach is essential due to multiple conditions that mimic IBD 3
• Consider medication-related causes (NSAIDs, anticoagulants) 3
• Cross-sectional imaging with CT is appropriate when abdominal pain is prominent 3

Critical Pitfalls to Avoid

• Never assume all rectal bleeding is from hemorrhoids without direct visualization, especially with recent systemic illness or in elderly patients 5
• Do not miss upper GI sources: 10-15% of severe hematochezia originates above the ligament of Treitz 5, 4
• Do not delay imaging in unstable patients while attempting bowel preparation for colonoscopy 5
• Do not perform colonoscopy as initial approach in hemodynamically unstable patients (shock index >1) 1
• In elderly patients, failure to consider non-IBD diagnoses (cancer, ischemia, medication-related) can lead to inappropriate management 3

Special Diagnostic Considerations

When Imaging is Indicated Beyond Standard Endoscopy

• CT scan, MRI, or endoanal ultrasound should be performed only if there is suspicion of concomitant anorectal diseases (sepsis/abscess, IBD, neoplasm) in patients with suspected complicated hemorrhoids 3
• Contrast-enhanced abdomino-pelvic CT scan for irreducible or strangulated rectal prolapse in stable patients to detect complications 3

Laboratory Risk Stratification

• Hemoglobin levels are critical for risk stratification using the Oakland score 1, 2
• Elevated inflammatory markers (CRP, procalcitonin, lactate) suggest bowel ischemia or necrosis 3
• Leukocytosis is a potential predictor for transmural bowel necrosis, except in immunocompromised patients 3

Transfusion and Anticoagulation Management

• Use restrictive transfusion thresholds: Hemoglobin trigger 70 g/L, target 70-90 g/L for patients without cardiovascular disease 1, 2, 5
• Higher threshold for cardiovascular disease: Hemoglobin trigger 80 g/L, target 100 g/L 1, 2
• For patients on warfarin with unstable bleeding: interrupt warfarin immediately and reverse with prothrombin complex concentrate and vitamin K 1, 2
• Restart warfarin 7 days after hemorrhage in patients with low thrombotic risk 1, 2

Prognosis Context

• Mortality in lower GI bleeding is generally related to comorbidity rather than exsanguination 1
• Overall in-hospital mortality is 3.4%, but rises to 18% for inpatient-onset bleeding and 20% for patients requiring ≥4 units of red cells 1
• Acute lower GI bleeding stops spontaneously in 75-90% of patients 7