What are the differential diagnoses and diagnostic approaches for rectal bleeding?

Rectal Bleeding: Differential Diagnoses and Diagnostic Approach

All patients over 40 years presenting with rectal bleeding require colonoscopy to exclude serious pathology, as 44% will have significant disease including colorectal cancer (8%), polyps ≥5mm (17%), or inflammatory bowel disease (11%). 1

Initial Assessment and Risk Stratification

Perform a focused history, vital signs assessment, digital rectal examination, and obtain hemoglobin, hematocrit, and coagulation studies immediately. 2, 3

Calculate the Oakland Score for risk stratification 2:

• Age: <40 (0 points), 40-69 (1 point), ≥70 (2 points)
• Gender: Female (0), Male (1)
• Previous LGIB admission: No (0), Yes (1)
• Blood on DRE: No (0), Yes (1)
• Heart rate: <70 (0), 70-89 (1), 90-109 (2), ≥110 (3)
• Systolic BP: <90 (5), 90-119 (4), 120-129 (3), 130-159 (2), ≥160 (0)
• Hemoglobin: <70 g/L (22), 70-89 (17), 90-109 (13), 110-129 (8), 130-159 (4), ≥160 (0)

Calculate shock index (heart rate/systolic BP) to identify active bleeding—a value >1 indicates hemodynamic instability requiring urgent intervention. 2

Differential Diagnoses by Prevalence

Common Benign Causes (55-84% of cases) 1, 4:

• Hemorrhoids (28-36% of cases) 1, 4
• Diverticular disease (16-27% of cases) 1, 4
• Anal fissures 5
• Benign anorectal conditions (16.7% in national audit) 2

Serious Pathology Requiring Intervention (44% of cases) 1:

• Colorectal carcinoma (8% of patients >40 years; 6% overall LGIB presentations) 2, 1
• Polyps ≥5mm (17% of patients) 1
• Inflammatory bowel disease (11% of patients) 1
• Arteriovenous malformations 4
• Anorectal varices (in patients with portal hypertension; bleeding occurs in <5% but can be fatal) 2

Specialized Causes 2, 5:

• Radiation-induced proctitis (in cancer treatment patients) 2
• Infectious proctitis 5
• Sexually transmitted disease-associated proctitis 5
• Ischemic proctitis 5
• Prolapse-induced proctitis 5

Diagnostic Algorithm

For Hemodynamically Unstable Patients (Oakland Score >8 or Shock Index >1):

1. Perform CT angiography (CTA) immediately as the first-line investigation 2, 3

• CTA has 79-95% sensitivity and 95-100% specificity for active bleeding 3
• Provides rapid localization without bowel preparation 2
• Useful for preoperative planning before embolization or surgery 2

2. Consider upper endoscopy urgently if CTA is negative, as bright red rectal bleeding with hemodynamic instability may indicate upper GI bleeding 2, 3

• Risk factors for UGIB source include: peptic ulcer disease history, portal hypertension, elevated BUN/creatinine ratio, antiplatelet drug use 2

3. Admit to hospital for colonoscopy on the next available list if patient stabilizes 2

For Hemodynamically Stable Patients with Major Bleeding (Oakland Score >8):

Admit to hospital for inpatient colonoscopy on the next available list with polyethylene glycol bowel preparation 2

• Colonoscopy has 42-90% diagnostic yield 2, 3
• No evidence supports urgent colonoscopy <24 hours over next-available-list timing 2
• Polyethylene glycol preparation superior to enemas for diagnostic yield 2

For Stable Patients with Minor Self-Terminating Bleeding (Oakland Score ≤8):

Discharge for urgent outpatient colonoscopy 2, 3

Critical timing considerations:

• Patients >50 years require colonoscopy within 2 weeks due to 6% cancer risk 2, 3
• All patients >40 years require full colonoscopy regardless of symptoms 1, 6

Anorectal Examination in All Patients:

Perform direct anorectal inspection using proctoscopy, rigid sigmoidoscopy, or flexible endoscopy with retroflexion to identify hemorrhoids, fissures, masses, and vascular abnormalities 2

• Benign anorectal conditions account for 16.7% of diagnoses 2
• Rectal examination findings do NOT predict colonoscopy findings—52% with normal rectal exams have significant pathology on colonoscopy 4

When Initial Investigations Are Negative

Second-Line Investigations 2, 3:

1. Endoscopic ultrasound (EUS) with color Doppler for suspected deep rectal varices 2, 3

• EUS detects rectal varices in 85% vs 45% for endoscopy alone 2
• Particularly valuable in patients with portal hypertension history 2

2. Video capsule endoscopy (VCE) for overt-obscure GI bleeding after negative upper and lower endoscopy 2

• Diagnostic yield 50-72% for obscure overt bleeding 2
• Highest yield when performed close to bleeding episode 2

3. Nuclear medicine red cell scintigraphy for intermittent or slow bleeding 2

• Sensitivity 60-93% 2
• Useful when CTA, angiography, or colonoscopy are negative 2

4. Repeat CTA only if bleeding becomes more brisk 2

• No benefit to routine repeat CTA after initial negative study 2

Critical Clinical Pitfalls

Symptoms are unreliable for risk stratification 1, 7:

• Only 3 symptoms significantly predict serious disease: blood mixed with stool (P<0.001), change in bowel habit (P<0.005), and abdominal pain (P<0.025) 1
• Symptoms change significantly between GP consultation and colonoscopy 1
• 96% of patients presenting with rectal bleeding do NOT have cancer 7

However, specific high-risk combinations exist 7:

• Rectal bleeding + change in bowel habit = 9.2% cancer prevalence 7
• Rectal bleeding without perianal symptoms = 11.1% cancer prevalence 7
• 36% of cancer patients have palpable rectal mass on examination 7

Documentation and follow-through failures are common 6:

• Colorectal cancer risk factors documented only 9-66% of the time 6
• Only 74% of patients needing colonoscopy receive orders, and only 56% complete it within one year 6
• Each unrelated primary care visit decreases odds of receiving recommended colonoscopy (OR 0.85) 6

Special Populations

Patients with Portal Hypertension and Suspected Anorectal Varices 2:

• Obtain focused history for long-standing portal hypertension 2
• Perform EUS with color Doppler as second-line diagnostic tool 2
• If EUS unavailable or negative, perform contrast-enhanced CT 2
• In pregnant patients, use MRI angiography if ultrasound fails 2

Patients with History of Pelvic Radiation 2:

• Consider radiation-induced proctitis with telangiectasia 2
• Flexible endoscopy required to determine bleeding cause 2
• If bleeding affects quality of life, optimize bowel function first, then consider sucralfate enemas (2g in 30-50ml water twice daily) 2
• Argon plasma coagulation has 7-26% serious complication rate in this population 2