Methods for diagnosing bile acid malabsorption: a systematic review.

BACKGROUND: Bile acid malabsorption (BAM) and bile acid-related diarrhea represent an under-recognized cause of chronic diarrhea mainly because of limited guidance on appropriate diagnostic and laboratory tests. We aimed to perform a systematic review of the literature in order to identify and compare the diagnostic accuracy of different diagnostic methods for patients with BAM, despite a proven gold standard test is still lacking. METHODS: A PubMed literature review and a manual search were carried out. Relevant full papers, evaluating the diagnostic accuracy of different methods for BAM, were assessed. Available data were analyzed to estimate the sensitivity and specificity of each published test. RESULTS: Overall, more than one test was considered in published papers on BAM. The search strategy retrieved 574 articles; of these, only 16 were full papers (with a total of 2.332 patients) included in the final review. Specifically, n = 8 studies used 75Selenium-homotaurocholic-acid-test (75SeHCAT) with a < 10% retention threshold; n = 8 studies evaluated fasting serum 7-α-hydroxy-4-cholesten-3-one (C4); n = 3 studies involved total fecal bile acid (BA) excretion over 48 h; n = 4 studies assessed fibroblast growth factor 19 (FGF19). 75SeHCAT showed an average sensitivity and specificity of 87.32 and 93.2%, respectively, followed by serum C4 (85.2 and 71.1%) and total fecal BA (66.6 and 79.3%). Fasting serum FGF19 had the lowest sensitivity and specificity (63.8 and 72.3%). All the extracted data were associated with substantial heterogeneity. CONCLUSIONS: Our systematic review indicates that 75SeHCAT has the highest diagnostic accuracy for BAM, followed by serum C4 assay. The diagnostic yield of fecal BA and FGF19 assays is still under investigation. Our review reinforces the need for novel biomarkers aimed to an objective detection of BAM and therefore improving the management of this condition.

Bile acid profiles within the enterohepatic circulation in a diabetic rat model after bariatric surgeries.

Bile acids (BAs), which are synthesized in the liver and cycled in the enterohepatic circulation, have been recognized as signaling molecules by activating their receptors in the intestine and liver. Serum taurine-conjugated BAs have been shown to be elevated after bariatric surgeries although the postoperative BA profiles within the enterohepatic circulation have not been investigated. Clarification of these profiles could help explain the mechanisms by which bariatric surgery leads to BA profile alterations and subsequent metabolic effects. We performed duodenal-jejunal bypass (DJB), sleeve gastrectomy (SG), and sham procedures in an obese diabetic rat model induced by high-fat diet and streptozotocin. The weight loss and antidiabetic effects were evaluated postsurgery. BA profiles in the systemic serum and within the enterohepatic circulation were analyzed, together with the expression of related BA transporters and enzymes at week 12 after surgery. Compared with sham, SG induced sustained weight loss, and both DJB and SG significantly improved glucose tolerance and insulin sensitivity with enhanced glucagon-like peptide 1 secretion. Similar to changes in the serum, BAs, especially taurine-conjugated species, were also elevated in the enterohepatic circulation (bile and portal vein) after DJB and SG. In addition, the expression of key BA transporters and conjugational enzymes was elevated postoperatively, whereas the enzymes responsible for BA synthesis were decreased. In conclusion, DJB and SG elevated BA levels in the systemic serum and enterohepatic circulation, especially taurine-conjugated species, which likely indicates increased ileal reabsorption and hepatic conjugation rather than synthesis. NEW & NOTEWORTHY Bile acids (BAs) have been implicated as potential mediators of the weight-independent effects of bariatric surgery. For the first time, we discovered that duodenal-jejunal bypass and sleeve gastrectomy elevated BAs, particularly the taurine-conjugated species in the enterohepatic circulation, likely through the promotion of ileal reabsorption and hepatic conjugation rather than BA synthesis. These findings will improve our understanding of BA metabolism after bariatric surgery and their subsequent metabolic effects.