Diagnosing patients with chronic watery diarrhea can be difficult for health care providers, since several causes with specific therapies, such as inflammatory bowel disease (IBD), microscopic colitis and chronic infection, need to be ruled out. A new clinical guideline1 (superscript 1) from the American Gastroenterological Association (AGA) published in Gastroenterology, the official journal of the AGA Institute, provides recommendations on the appropriate laboratory tests based on current evidence to exclude other diagnoses in the setting of suspected functional diarrhea or irritable bowel syndrome with diarrhea (IBS-D).
When managing patients with chronic watery diarrhea, it is important for health care providers to determine whether it is being caused by organic disease or a functional disorder, such as functional diarrhea or irritable bowel syndrome with 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. 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.” Walter Smalley, MD, MPH, first author, Veterans Affairs Tennessee Valley Healthcare System and Vanderbilt University School of Medicine, Nashville, Tennessee
The AGA guideline applies to patients with properly working immune systems who have “watery” diarrhea of at least four weeks duration. It excludes patients with bloody diarrhea; diarrhea with signs of poor fat absorption; features of alarm symptoms, such as weight loss, anemia and hypoalbuminemia; a family history of IBD, colon cancer or celiac disease; and those with a travel history to regions where diarrhea-related diseases are common.
The guideline recommends considering the use of the following laboratory tests for the evaluation of functional diarrhea and IBS-D in adults:
1. In patients presenting with chronic diarrhea, AGA suggests the use of either fecal calprotectin or fecal lactoferrin, which have been proposed as markers for inflammatory conditions, such as IBD. (Conditional recommendation; low quality evidence)
2. In patients presenting with chronic diarrhea, AGA suggests against the use of erythrocyte sedimentation rate or C-reactive protein to screen for IBD. (Conditional recommendation: low evidence)
3. In patients presenting with chronic diarrhea, AGA recommends testing for Giardia, a common cause of watery diarrhea that can be readily treated. (Strong recommendation: high quality evidence)
4. In patients presenting with chronic diarrhea with no travel history to or recent immigration from high risk areas, AGA suggests against testing for ova and parasites (other than Giardia). (Conditional recommendation: low quality evidence)
5. In patients presenting with chronic diarrhea, AGA recommends testing for celiac disease with IgA tissue transglutaminase and a second test to detect celiac disease in the setting of IgA deficiency. Celiac disease is an important cause of chronic diarrhea. (Strong recommendation: moderate quality evidence)
6. In patients presenting with chronic diarrhea, AGA suggests testing for bile acid diarrhea, which may be due to excess production or decreased absorption of bile acids, which then reach the colon and can cause watery diarrhea. (Conditional recommendation: low quality evidence)
7. In patients presenting with chronic diarrhea, AGA makes no recommendation for the use of currently available serologic tests for diagnosis of IBS. (No recommendation; knowledge gap)