What is the appropriate workup for a patient with chronic diarrhea (diarrhea lasting more than 2 months)?

Diagnostic Workup for Chronic Diarrhea (10 Times Daily for 2 Months)

The appropriate workup for a patient with chronic diarrhea (10 times daily for 2 months) should begin with a detailed history, physical examination, and basic laboratory tests, followed by targeted investigations based on the suspected type of diarrhea (inflammatory, malabsorptive, or secretory).

Initial Assessment

• Chronic diarrhea is defined as abnormal passage of ≥3 loose stools per day for more than 4 weeks 1, 2
• Evaluate for alarm features: nocturnal diarrhea, weight loss, blood in stool, fever, and recent onset (<3 months) 1
• Assess for risk factors including family history of neoplastic, inflammatory bowel, or celiac disease 1, 2
• Review medication history to identify potential diarrheogenic agents 1
• Evaluate previous surgical history, especially involving the ileum, right colon, or gastric bypass 1, 2

First-Line Investigations (Primary Care)

• Complete blood count, C-reactive protein, electrolytes, liver function tests, iron studies, vitamin B12, folate, and thyroid function 1, 3
• Serum anti-tissue transglutaminase IgA and total IgA to screen for celiac disease 1, 2
• Stool studies:
  • Fecal calprotectin to exclude inflammatory causes 1, 2
  • Stool culture and microscopy if infectious etiology suspected 1, 3
  • Fecal immunochemical test (FIT) to help exclude colorectal cancer 1

Categorizing Diarrhea Type

Based on initial findings, categorize the diarrhea as:

Watery Diarrhea

• Measure fecal osmotic gap to distinguish between secretory (<50 mOsm/kg) and osmotic (>125 mOsm/kg) diarrhea 4, 5
• For suspected secretory diarrhea:
  • Test for bile acid malabsorption with SeHCAT or serum 7α-hydroxy-4-cholesten-3-one 1, 2
  • Consider endocrine causes (thyroid function tests, serum peptide concentrations if clinically indicated) 4, 6

Fatty Diarrhea (Steatorrhea)

• If malabsorption suspected:
  • Endoscopic distal duodenal biopsies to exclude small bowel enteropathy 1, 3
  • Tests for pancreatic insufficiency (fecal elastase) 1

Inflammatory Diarrhea

• Colonoscopy with biopsies (age-stratified approach) 1
  • Full colonoscopy recommended for patients >45 years 1
  • Flexible sigmoidoscopy may be sufficient for younger patients without alarm features 1
• Biopsies to evaluate for microscopic colitis, especially in older patients with normal endoscopic appearance 2, 3

Special Considerations

• For patients <40 years without alarm features and normal fecal calprotectin, avoid immediate colonoscopy 1
• For persistent undiagnosed diarrhea despite initial workup, consider:
  • Small bowel bacterial overgrowth testing (glucose or lactulose hydrogen breath test) 1, 6
  • Laxative screening if factitious diarrhea suspected 1, 5
  • CT enterography or MR enterography if small bowel pathology suspected 6, 3

Common Pitfalls to Avoid

• Failing to distinguish between functional disorders (IBS) and organic disease 2, 6
• Overlooking microscopic colitis, which presents similar to IBS but requires different treatment 2
• Missing bile acid malabsorption, which is common but often underdiagnosed 1, 2
• Neglecting to test for celiac disease, which has variable presentations 1, 3

By following this systematic approach, the majority of cases of chronic diarrhea can be diagnosed and appropriate treatment initiated, improving morbidity, mortality, and quality of life outcomes.