Initial lab results: (Per AGA guidelines on limited evaluation of patients with suspected functional diarrhea/IBS-D)
Calprotectin 635
Giardia Ag negative
TTG negative, total IgA level normal
Discussion, Part 1
Her initial presentation of chronic non-bloody diarrhea has a broad differential diagnosis, including functional diarrhea, irritable bowel syndrome with diarrhea, small intestinal bacterial overgrowth, and inflammatory bowel disease. A functional diagnosis is likely higher on the initial differential diagnosis given the absence of any alarm features such as bloody diarrhea or weight loss, as well as an unremarkable family history.
The AGA recommends a limited laboratory evaluation to exclude other causes of diarrhea in patients with suspected functional diarrhea or irritable bowel syndrome [1]. Calprotectin is the preferred screening test for IBD in this setting. Using a threshold of 50 ug/g, the sensitivity and specificity of this test for detecting IBD is estimated at 0.81 and 0.87, respectively [2]. By contrast, routine use of the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as a screening test for IBD is not recommended given its inferior performance characteristics; the estimated sensitivity and specificity of CRP for identifying a patient with IBD among those with diarrhea are 0.73 and 0.78, respectively.
Routine testing for Giardia is recommended given its prevalence in the United States but testing for other ova and parasites is not recommended in the absence of any travel history. Finally, testing for celiac disease with IgA tissue transglutaminase is recommended. A total IgA level should also be checked to rule out IgA deficiency as a cause for a negative test. In patients with IgA deficiency, alternative testing for celiac disease can be performed, such as IgG deaminated gliadin peptides. Routine use of serologic markers for IBD is not indicated given their poor sensitivity [3].
Given the elevated calprotectin, colonoscopy is indicated in this case to evaluate for possible IBD.
References
- Smalley et al. AGA Clinical Practice Guidelines on the Laboratory Evaluation of Functional Diarrhea and Diarrhea-Predominant Irritable Bowel Syndrome in Adults (IBS-D). Gastro 2019;157(3):851-854.
- Carrasco-Labra A et al. AGA Technical Review on the Evaluation of Functional Diarrhea and Diarrhea-Predominant Irritable Bowel Syndrome in Adults (IBS-D). Gastro 2019;157(3):859-880.
- Mitsuyama K et al. Antibody markers in the diagnosis of inflammatory bowel disease. World J Gastroenterol 2016;22:1304-1310.
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