What is the algorithmic approach for managing chronic diarrhea?

Algorithmic Approach for Chronic Diarrhea

Begin with a detailed history focusing on alarm features (blood in stool, unintentional weight loss, nocturnal symptoms, duration <3 months), followed immediately by first-line laboratory testing including complete blood count, C-reactive protein, IgA tissue transglutaminase with total IgA level, and stool testing for Giardia antigen. 1, 2

Step 1: Initial History and Risk Stratification

Identify Alarm Features (Mandate Aggressive Workup)

• Blood in stool, unintentional weight loss, fever, or nocturnal diarrhea indicate organic disease and require urgent colonoscopy with biopsies due to high risk of colorectal cancer (27% prevalence in patients with bowel habit changes) and inflammatory bowel disease 1, 2
• Age >50 years mandates colonoscopy regardless of other features, as approximately 50% of neoplasia occurs proximal to splenic flexure 1
• Symptoms <3 months duration suggest organic rather than functional disease 3, 2

Assess Specific Risk Factors

• Prior terminal ileal resection, cholecystectomy, or abdominal radiotherapy strongly suggest bile acid diarrhea and warrant SeHCAT testing (if available) or empiric trial of cholestyramine 2
• Family history of inflammatory bowel disease, celiac disease, or colorectal cancer increases pretest probability 3
• Recent travel or immigration from high-risk areas changes testing approach to include broader infectious workup 2
• Medication review is mandatory—proton pump inhibitors, antibiotics, and metformin are common culprits 2

Distinguish Stool Characteristics

• Bulky, pale, malodorous stools suggest malabsorption/steatorrhea 3
• Liquid loose stools with blood or mucus suggest colonic/inflammatory etiology 3

Step 2: First-Line Laboratory Testing (Complete Within 1-2 Weeks)

Mandatory Tests for All Patients

• IgA tissue transglutaminase PLUS total IgA level (sensitivity/specificity >90% for celiac disease; total IgA detects IgA deficiency which causes false-negative results) 1, 2
• Giardia antigen test or PCR (sensitivity/specificity >95%) 2
• Complete blood count and C-reactive protein to screen for inflammation and anemia 2
• Fecal calprotectin to distinguish inflammatory from non-inflammatory causes (elevated in IBD and microscopic colitis) 1, 2

Additional Testing Based on Risk Factors

• Stool culture and ova/parasites only if recent travel history (extremely low yield in immunocompetent patients without travel) 2
• Fecal occult blood or FIT testing increases sensitivity for colorectal neoplasia 1

Step 3: Endoscopic Evaluation

Colonoscopy with Biopsies (Schedule Within 2-4 Weeks if Alarm Features Present)

• Mandatory for patients with weight loss, age >50 years, or elevated inflammatory markers (diagnostic yield 7-31%) 1
• Must be full colonoscopy, not flexible sigmoidoscopy alone, as 50% of neoplasia is proximal to splenic flexure 1
• Obtain biopsies even with normal-appearing mucosa to detect microscopic colitis (15% of chronic diarrhea in older adults, particularly women) 1
• Aim for >90% cecal intubation rate with terminal ileal intubation 3

Upper Endoscopy with Duodenal Biopsies

• Perform when celiac serology is positive to confirm diagnosis 2
• Consider if initial workup unrevealing and symptoms persist (proceed within 4-6 weeks) 1

Step 4: Categorize Diarrhea Type and Pursue Targeted Testing

Watery Diarrhea (Subdivided into Three Types)

Secretory:

• Bile acid diarrhea: SeHCAT testing (preferred) or serum C4 assay; treat with cholestyramine 2
• Microscopic colitis: Diagnosed only by colonic biopsies 1
• Endocrine disorders: Consider if other features present 4

Osmotic:

• Lactose intolerance: Hydrogen breath testing; treat with lactose restriction or lactase supplements 2
• Laxative abuse: Stool/urine testing for laxatives 3

Functional:

• Irritable bowel syndrome: Diagnosis of exclusion only after negative workup; Rome IV criteria have only 52-74% specificity and do NOT reliably exclude IBD, microscopic colitis, or bile acid diarrhea 2
• NEVER diagnose IBS in patients with weight loss 1

Fatty Diarrhea (Malabsorption/Maldigestion)

• Celiac disease: Strict gluten-free diet after confirmation with duodenal biopsies 2
• Giardiasis: Treat with metronidazole or tinidazol short course 5
• Small bowel bacterial overgrowth: Empiric trial of antibiotics (rifaximin 550mg three times daily for 14 days for IBS-D) 2, 6
• Pancreatic insufficiency: Consider if risk factors present 4

Inflammatory Diarrhea

• Inflammatory bowel disease: Disease-modifying therapies based on type and severity 2
• Clostridioides difficile: Test if recent antibiotic exposure 4
• Colorectal cancer: Excluded by colonoscopy 1

Step 5: Symptomatic Management When Specific Cause Not Found or While Awaiting Diagnosis

Dietary Modifications

• Eliminate caffeine, alcohol, sorbitol, and fructose 2

Pharmacologic Options

• Loperamide (most common antidiarrheal; constipation occurs in 1.6-5.3% of patients) 7, 8
• Cholestyramine for bile acid diarrhea 2
• Bulking agents, probiotics, anticholinergics for refractory cases 8

Critical Pitfalls to Avoid

• Do NOT assume functional diarrhea based on Rome IV criteria alone—these have only 52-74% specificity 2
• Do NOT skip total IgA testing when ordering celiac serology—IgA deficiency causes false-negative IgA-tTG results 2
• Do NOT order broad ova/parasite panels without travel history—yield is extremely low 2
• Do NOT perform flexible sigmoidoscopy alone in patients with alarm features—full colonoscopy is required 1
• Do NOT skip colonic biopsies even with normal-appearing mucosa—microscopic colitis requires histologic diagnosis 1
• Do NOT overlook bile acid diarrhea in patients with prior cholecystectomy or ileal resection 2
• Do NOT diagnose IBS in any patient with weight loss—this is an absolute exclusion criterion 1