What a GI Stool Profile Includes
A comprehensive GI stool profile for evaluating chronic diarrhea should include fecal calprotectin (or fecal lactoferrin) to screen for inflammatory bowel disease, Giardia testing, and bile acid measurement when available, along with basic stool characteristics assessment. 1
Core Components Based on AGA Guidelines
The 2019 AGA guidelines provide the strongest framework for what should be included in stool testing for chronic diarrhea 1:
Inflammatory Markers (Conditional Recommendation)
- Fecal calprotectin (threshold ≥50 mg/g for optimal sensitivity) OR
- Fecal lactoferrin (threshold 4.0-7.25 mg/g)
- These markers screen for IBD with pooled sensitivity of 0.81 and specificity of 0.87 for calprotectin 1
- Do NOT use serum ESR or CRP for IBD screening—they have inferior performance 1
Parasitic Testing (Strong Recommendation)
- Giardia testing is strongly recommended (high-quality evidence) 1
- Testing can be done via antigen detection or PCR for Giardia small subunit ribosomal RNA
- Avoid routine ova and parasites testing unless there is travel history to or immigration from high-risk areas 1
Bile Acid Diarrhea Assessment (Conditional Recommendation)
- 48-hour stool collection for total bile acids (documents increased fecal bile acids) 1
- Serum fibroblast growth factor 19 (measures defective feedback of bile acid synthesis)
- Note: The homotaurocholic acid test (SeHCAT) is used in Europe but not available in North America 1
- The British Society of Gastroenterology recommends making a positive diagnosis rather than empirical treatment 2
Additional Stool Analyses for Specific Clinical Scenarios
When Malabsorption is Suspected
- Fecal elastase for pancreatic insufficiency evaluation 2
- Stool fat quantification (though not routinely part of initial screening)
Comprehensive Biochemical Analysis
When the diagnosis remains unclear after initial testing, comprehensive stool analysis can differentiate diarrhea subtypes 3, 4:
- Stool osmolality, pH, and electrolytes to distinguish osmotic from secretory diarrhea
- Stool form assessment using Bristol Stool Form Scale 5
Infection Screening in Acute-on-Chronic Presentations
Modern GI panels can detect up to 22 pathogens including bacteria, viruses, and parasites 6, though these are typically reserved for:
- Symptoms >7 days with high pretest probability of infection
- Immunocompromised patients
3 unformed stools per 24 hours with systemic symptoms 3
Critical Pitfalls to Avoid
Do not order routine stool cultures or ova and parasites panels in chronic diarrhea without travel history—the yield is extremely low and not cost-effective 1. The exception is Giardia, which should always be tested.
Fecal calprotectin is most useful in patients under age 40 to exclude colonic inflammation when IBS is suspected 2. A threshold of 50 mg/g optimizes sensitivity while maintaining reasonable specificity 1.
Bile acid testing availability varies significantly by region. If testing is unavailable, the AGA notes it is reasonable to use an empirical trial of bile acid binders, though the British guidelines argue against this approach 1, 2.
What NOT to Include
- Serologic tests for IBS diagnosis (insufficient evidence—knowledge gap per AGA) 1
- Routine breath testing for small bowel bacterial overgrowth (insufficient evidence; empirical antibiotic trial preferred) 2
- Small bowel barium studies (poor sensitivity and specificity) 2
The stool profile should be tailored based on clinical presentation: inflammatory diarrhea (bloody, mucoid) warrants calprotectin; watery diarrhea with weight loss suggests malabsorption testing; and frequent low-volume stools point toward bile acid diarrhea assessment 7.