The BACH project protocol: an international multicentre total Bile Acid Comparison and Harmonisation project and sub-study of the TURRIFIC randomised trial

Multicentre international trials relying on diagnoses derived from biochemical results may overlook the importance of assay standardisation from the participating laboratories. Here we describe a study protocol aimed at harmonising results from total bile acid determinations within the context of an international randomised controlled Trial of two treatments, URsodeoxycholic acid and RIFampicin, for women with severe early onset Intrahepatic Cholestasis of pregnancy (TURRIFIC), referred to as the Bile Acid Comparison and Harmonisation (BACH) study, with the aims of reducing inter-laboratory heterogeneity in total bile acid assays. We have simulated laboratory data to determine the feasibility of total bile acid recalibration using a reference set of patient samples with a consensus value approach and subsequently used regression-based techniques to transform the data. From these simulations, we have demonstrated that mathematical recalibration of total bile acid results is plausible, with a high probability of successfully harmonising results across participating laboratories. Standardisation of bile acid results facilitates the commutability of laboratory results and collation for statistical analysis. It may provide the momentum for broader application of the described techniques in the setting of large-scale multinational clinical trials dependent on results from non-standardised assays.