AGA Develops Guideline for the Laboratory Evaluation of Functional Diarrhea, IBS-D

The American Gastroenterological Association (AGA) has released a clinical practice guideline on the laboratory evaluation of functional diarrhea and diarrhea-predominant irritable bowel syndrome (IBS-D) in adults. The guideline includes recommendations and suggestions on how clinicians can select the appropriate laboratory tests to exclude other diagnoses in the setting of suspected functional diarrhea or IBS-D.1

According to the authors, the guideline applies to the evaluation of persons who are immunocompetent and who have had “watery” diarrhea for at least 4 weeks. The guideline should not be followed when managing patients with bloody diarrhea, diarrhea with signs of fat malabsorption, and patients with a family history of inflammatory bowel disease (IBD), colon cancer, or celiac disease.

The guideline developed by the panel included the following recommendations, based on strong evidence, for patients with chronic diarrhea:

  • The AGA recommends testing for Giardia. Use of a Giardia antigen test or polymerase chain reaction for Giardia test is recommended.
  • The AGA recommends testing for celiac disease with IgA tissue transglutaminase and a second test to detect celiac disease in the setting of IgA deficiency.

The guideline developed by the panel also included the following suggestions, based on conditional or low evidence, for patients with chronic diarrhea: 

  • The AGA suggests that clinicians test for bile acid diarrhea; an empiric trial of a bile acid binder can be considered for use in settings with limited availability of commercial assays.
  • The AGA suggests the use of either fecal calprotectin or fecal lactoferrin to screen for IBD. 
  • The AGA suggests against the use of erythrocyte sedimentation rate or C-reactive protein to screen for IBD.
  • The AGA suggests against testing for ova and parasites among patients with no travel history to or recent immigration from high-risk areas.

The AGA made no recommendation for the use of currently available serologic tests for the diagnosis of IBS in patients who present with chronic diarrhea.

“Both functional diarrhea and IBS-D are clinical diagnoses with no defining laboratory tests. A workup to exclude all organic disease is impractical, expensive, and potentially dangerous to patients if false-positive tests result in further invasive testing,” guideline first author Walter Smalley, MD, MPH, said in a press release issued by the AGA. “The AGA guideline on evaluation of chronic diarrhea is intended to reduce practice variation and promote high-quality and high-value care for this patient population.”2

—Colleen Murphy


1. Smalley W, Falck-Ytter C, Carrasco-Labra A, Wani S, Lytvyn l, Falck-Ytter Y. AGA clinical practice guidelines on the laboratory evaluation of functional diarrhea and diarrhea-predominant irritable bowel syndrome in adults (IBS-D). Gastroenterology. 2019;157(3):851-854. doi:10.1053/j.gastro.2019.07.004.

2. AGA releases guideline on the evaluation of chronic diarrhea [press release]. Bethesda, MD: American Gastroenterological Association; September 23, 2019. Accessed September 24, 2019.