Chronic diarrhea of functional etiology is a commonly encountered outpatient GI diagnosis. Unfortunately, the optimal laboratory evaluation of chronic diarrhea is not standardized. In the present article, the American Gastroenterological Association (AGA) provides recommendations for assessment of suspected functional diarrhea or diarrhea-predominant IBS (IBS-D). These recommendations apply to patients with watery diarrhea of at least 4 weeks duration and exclude those with alarm features, such as bleeding, steatorrhea, weight loss, anemia, or hypoalbuminemia. Further excluded are patients with a family history of colon cancer, celiac disease, or recent travel to regions with endemic enteric pathogens.
- Consider ordering fecal calprotectin or fecal lactoferrin to screen for IBD. The recommendation is conditional, and the evidence is low quality.
- Routinely ordering an erythrocyte sedimentation rate or C-reactive protein is not recommended to screen for IBD. The recommendation is conditional, and the evidence is low quality.
- Testing for Giardia using either the Giardia antigen test or polymerase chain reaction is recommended. The recommendation is strong, and the evidence is high quality.
- Routine testing for ova and parasites (other than Giardia) is not recommended in patients with no history of travel to high-risk areas. The recommendation is conditional, and the evidence is low quality.
- Testing for celiac disease with tissue transglutaminase IgA and total serum IgA is recommended. The recommendation is strong, and the evidence is moderate quality.
- Consider testing for bile acid diarrhea. This may entail an empiric trial of bile acid binders, especially when specific laboratory testing is not available. The recommendation is conditional, and the evidence is low quality.
- Routine testing with serologic tests for a diagnosis of postinfectious IBS-D is not recommended. There is insufficient evidence for a recommendation.
Smalley W, Falck-Ytter C, Carrasco-Labra A, Wani S, Lytvyn L, Falck-Ytter Y. AGA guideline on the laboratory evaluation of functional diarrhea and diarrhea-predominant irritable bowel syndrome in adults (IBS-D). Gastroenterology
2019 July 11. (Epub ahead of print) (https://doi.org/10.1053/j.gastro.2019.07.004