A new set of guidelines for adults with Diarrhea-Predominant Irritable Bowel Syndrome (IBS-D)
will aid clinicians in choosing the appropriate laboratory tests to diagnose the disease.
A committee, led by Walter Smalley, MD, Vanderbilt University School of Medicine, has presented new recommendations approved by the American Gastroenterological Association (AGA) for the evaluation of the immunocompetent patient with “watery” diarrhea for at least 4 weeks.
The new guidelines do not apply to patients with bloody diarrhea, diarrhea with signs of fat malabsorption, and presentations with alarm features like weight loss, anemia, and hypoalbuminemia.
The guidelines also exclude patients with a family history of inflammatory bowel disease, colon cancer, or celiac disease, and patients with a travel history to regions with recognized specific diarrhea-related pathogens.
The investigators identified a pair of markers for inflammatory conditions—calprotectin and fecal lactoferrin—that they recommend testing for to derive at a diagnosis.
“There are several studies using fecal calprotectin with different threshold values to identify persons with IBD,” the authors wrote. “Based on a review of the available data, it appears that using fecal calprotectin with a threshold of 50 μg/g yields the optimal performance.”
Fecal lactoferrin has been studied as a marker for IBD, but low quality of evidence supporting the use of these tests is compounded with the low likelihood that a positive test would initiate further confirmatory evaluation.
This leads to an earlier diagnosis of IBD compared to the 10% likelihood that someone without IBD may needlessly be exposed to further confirmatory testing.
For patients with chronic diarrhea, the AGA recommends against using erythrocyte sedimentation rate or C-reactive protein to screen for IBD.
For this patient population, the guidelines call for testing for Giardia, a microscopic parasite known to cause diarrheal illness.
Specifically for patients without a travel history or recent immigration from high-risk areas, the AGA suggests against testing for ova and parasites other than Giardia.
Another recommendation includes 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 and other manifestations,” the authors wrote. “Among patients with chronic diarrhea who do not have IgA deficiency, use of serum IgA tissue transglutaminase (tTG) is a highly efficient strategy for determining the presence of celiac disease.”
IgA deficiency can also lead to a false-negative result, which is negated by the 2 recommended tests.
The taskforce also concluded that testing for bile acid diarrhea is appropriate for chronic diarrhea patients.
Bile acid diarrhea may be due to excess production or decreased absorption of bile acids, which then reach the colon, causing watery diarrhea.
There are currently several tests available for this, including a selenium homotaurocholic acid test, which is primarily used in Europe, and measuring total bile acids in a 48-hour stool collection, the test of choice in the US.
The new guidelines are set to expire in 5 years.
The study, “AGA Clinical Practice Guidelines on the Laboratory Evaluation of Functional Diarrhea and Diarrhea-Predominant Irritable Bowel Syndrome in Adults (IBS-D
),” was published online in Gastroenterology