Loading...
Functional diarrhea (FD) and diarrhea-predominant irritable bowel syndrome (IBS-D) are highly prevalent disorders that can be difficult to distinguish from organic causes of chronic diarrhea (i.e., lasting >4 weeks) based on symptoms alone. Clinicians often use an array of biomarkers to assist diagnosis; however, there is little available guidance regarding the appropriate use of available diagnostic tests. This guideline provides evidence-based recommendations addressing these gaps.
Test for celiac disease with immunoglobulin A (IgA) tissue transglutaminase. In the case of IgA deficiency, immunoglobulin G (IgG) tissue transglutaminase and IgG or IgA deaminated gliadin peptides can be measured.
Test for Giardia infection using antigen test or polymerase chain reaction.
Consider testing for bile acid diarrhea. If assays are unavailable, empiric treatment with a bile acid binder is reasonable.
Use either fecal calprotectin (threshold, 50 μg/g) or fecal lactoferrin (threshold range, 4.0–7.25 μg/g) to screen for inflammatory bowel disease (IBD).
Do not measure erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to screen for IBD, although CRP can be considered as an alternative to fecal calprotectin or lactoferrin if these cannot be measured.
Do not test for ova and parasites in the absence of a suggestive travel or immigration history.
The routine measurement of serological markers of IBS (antibodies to cytolethal distending toxin B and the gut mucosal protein vinculin) awaits additional supportive data.
Smalley W et al. AGA guideline on the laboratory evaluation of functional diarrhea and diarrhea-predominant irritable bowel syndrome in adults (IBS-D). Gastroenterology 2019 Jul 11; [e-pub]. (https://doi.org/10.1053/j.gastro.2019.07.004)
Comment
These guidelines are based on an informative technical review of each diagnostic test (Gastroenterology 2019 Jul 25; [e-pub]) and provide practical guidance for primary care and GI providers. Take-home points are to avoid the “kitchen sink” approach where multiple tests are done simultaneously in patients with suspected FD or IBS-D, and rather to focus first on celiac disease, Giardia infection, and stool inflammatory markers. An empiric trial of bile acid binders is a reasonable concomitant or subsequent step, as diagnostic tests for bile acid diarrhea are either not available or not widely used. Older patients with chronic watery diarrhea should be considered for endoscopic evaluation with biopsy to exclude microscopic colitis.