title: A Multicenter Prospective Study to Investigate the Diagnostic Accuracy of the SeHCAT Test in Measuring Bile Acid Malabsorption: Research Protocol.
abstract: BACKGROUND
  Bile acid malabsorption (BAM) is one possible explanation for chronic diarrhea. BAM may be idiopathic, or result from ileal resection or inflammation including Crohn's disease, or may be secondary to other conditions, including cholecystectomy, peptic ulcer surgery, and chronic pancreatitis. No "gold standard" exists for clinical diagnosis of BAM, but response to treatment with a bile acid sequestrant (BAS) is often accepted as confirmation. The SeHCAT (tauroselcholic [selenium-75] acid) test uses a radiolabeled synthetic bile acid and provides a diagnostic test for BAM, but its performance against "trial of treatment" is unknown. Fibroblast growth factor 19 (FGF-19) and 7-alpha-hydroxy-4-cholesten-3-one (C4) also offer potential new biomarkers of BAM.
  
  
  OBJECTIVE
  This protocol describes a multicenter prospective study to evaluate the diagnostic accuracy of SeHCAT and 2 biomarkers in predicting BAM as assessed by trial of treatment.
  
  
  METHODS
  Participating gastroenterology centers should have a minimum workload of 30 SeHCAT patients per annum. Patients should not be pregnant, on medication that could confound follow-up, or have any severe comorbidity. All eligible patients attending a gastrointestinal appointment will be invited to participate. On attending the SeHCAT test, blood and fecal samples will be collected for analysis of FGF-19 by enzyme-linked immunosorbent assay and for C4 and fractionated bile acids by liquid chromatography-mass spectrometry. A capsule containing radiolabeled SeHCAT will be administered orally and a scan performed to measure SeHCAT activity. Patients will return on day 7 to undergo a second scan to measure percentage SeHCAT retention. The test result will be concealed from clinicians and patients. BAS will be dispensed to all patients, with a follow-up gastroenterologist appointment at 2 weeks for clinical assessment of treatment response and adherence. Patients responding positively will continue treatment for a further 2 weeks and all patients will have a final follow-up at 8 weeks. The diagnostic accuracy of the SeHCAT test and biomarkers will be analyzed at different thresholds using sensitivity, specificity, positive and negative predictive value, likelihood ratios, and area under the curve in a sample of 600 patients. Multivariable logistic regression models will be used to assess the association between presence of BAM and continuous SeHCAT retention levels after adjustment for confounders.
  
  
  RESULTS
  Funding is being sought to conduct this research.
  
  
  CONCLUSIONS
  The SeHCAT test for diagnosis of BAM has been in common use in the United Kingdom for more than 30 years and an evidence-based assessment of its accuracy is overdue. The proposed study has some challenges. Some forms of BAS treatment are unpleasant due to the texture and taste of the resin powder, which may negatively affect recruitment and treatment adherence. Trial of treatment is not as "golden" a standard as would be ideal, and itself warrants further study.
authors.affiliation: Division of Health and Social Care Research, King's College London, London, United Kingdom. fiona.reid@kcl.ac.uk.
authors.forename: Fiona
authors.identifier: http://orcid.org/0000-0002-0762-8111
authors.initials: F
authors.lastname: Reid
authors.forename: Janet
authors.identifier: http://orcid.org/0000-0002-0310-2518
authors.initials: J
authors.lastname: Peacock
authors.forename: Bola
authors.identifier: http://orcid.org/0000-0002-4403-0215
authors.initials: B
authors.lastname: Coker
authors.forename: Viktoria
authors.identifier: http://orcid.org/0000-0001-7204-6284
authors.initials: V
authors.lastname: McMillan
authors.forename: Cornelius
authors.identifier: http://orcid.org/0000-0003-0217-3266
authors.initials: C
authors.lastname: Lewis
authors.forename: Stephen
authors.identifier: http://orcid.org/0000-0002-0592-2122
authors.initials: S
authors.lastname: Keevil
authors.forename: Roy
authors.identifier: http://orcid.org/0000-0002-3983-311X
authors.initials: R
authors.lastname: Sherwood
authors.forename: Gill
authors.identifier: http://orcid.org/0000-0003-1090-1657
authors.initials: G
authors.lastname: Vivian
authors.forename: Robert
authors.identifier: http://orcid.org/0000-0002-4986-1077
authors.initials: R
authors.lastname: Logan
authors.forename: Jennifer
authors.identifier: http://orcid.org/0000-0002-3156-0479
authors.initials: J
authors.lastname: Summers
keywords: SeHCAT test; accuracy; bile acid malabsorption; bile acid sequestrant; diagnostic test; diarrhea
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