Excess bile acids entering the colon can cause the classic signs and symptoms of bile acid malabsorption (BAM), including watery stool, urgency, and fecal incontinence. While BAM has been associated with diarrhea for nearly 50 years, it remains an underrecognized and underdiagnosed cause of chronic diarrhea.
In a recent issue of Mayo Clinic's Digestive Diseases, Michael Camilleri, M.D., a gastroenterologist at Mayo Clinic, and Leslie Donato, Ph.D., Co-Director for Cardiovascular Laboratory Medicine, Hospital Clinical Laboratory, and Point of Care Testing at Mayo Clinic, discuss BAM testing in clinical practice.
According to Dr. Camilleri, "Bile acid diarrhea affects 1% or 2% of people in the community, which is the same approximate prevalence of celiac disease in the United States. However, there have been no readily available methods in the U.S. that directly measure it. The 75selenium homotaurocholic acid seven-day retention test (SeHCAT), which is validated and used in most European countries, is not available in the United States. The alternative has been a therapeutic trial of a bile sequestrant. But some of these drugs are poorly tolerated—especially resin formulations such as cholestyramine—the response is variable, and their use is difficult to justify without a definitive diagnosis. Today, however, there are two tests available in the U.S. for evaluating BAM—the serum 7αC4 test and the fecal bile acid test."
The fecal bile acid excretion test quantifies individual and total bile acids in a 48-hour stool collection. According to Dr. Donato, increased total fecal bile acids are seen in patients with chronic functional diarrhea, and higher levels of the primary bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA) are associated with IBS-D.
The second test option for BAM is the 7αC4 test, which measures fasting serum levels of the marker 7α-hydroxy-4-cholesten-3-one, abbreviated to 7αC4 or C4. Fasting serum C4 levels increase when bile acid synthesis increases, and C4 levels are substantially elevated in BAM patients. "The serum C4 test was not developed at Mayo, but our staff validated and refined the assays, proving that it's useful, and we now offer it as an orderable test," Dr. Donato said.
According to Dr. Camilleri, "We've conclusively demonstrated that about one-third of patients with chronic diarrhea thought to be due to IBS-D or functional diarrhea have BAM and need to be diagnosed properly and treated more specifically and effectively."
For more information on testing for bile acid malabsorption, view Mayo Medical Laboratories' free webinar: Testing Options for Patients with Chronic Diarrhea: A Focus on Bile Acid Malabsorption.