Biological, experimental and analytical determinants influencing bile acids concentrations in human blood: a review and meta-analysis.

BackgroundDespite over three decades of research, the use of peripheral bile acid concentrations or proportions as biomarkers for human liver injury remain inconclusive due to variable and inconsistent findings. ObjectiveThe aim of this systematic review and meta-analysis was to identify factors contributing to the variability in published bile acid research and propose recommendations to enhance the robustness and reproducibility of future studies. MethodsA search of the PubMed database and a systematic manual screening of references until May 2024 for studies reporting peripheral bile acid concentrations in humans was conducted. English-language studies reporting mean or median concentrations of at least one of 15 predetermined circulating bile acids in human cohorts were included. The exclusion criteria were editorials, commentaries, letters to the editor, conference proceedings, abstracts, and monographs. Raw bile acid concentrations, subject demographics (number, average age, sex distribution, health status, fasted/fed status), the blood matrix analysed, the matrix volume analysed, the bile acid extraction process, and analytical technique when available were extracted by a single observer. Results65 studies involving 215 cohorts were selected. Bile acid concentrations in normal cohorts exhibit large intervariability. The analytical technique used to measure bile acid concentrations, the fasted/fed status of patients at the time of sampling, the choice of blood collection matrix, the starting volume of this matrix, and the choice of protein precipitation solvent are found to be determinants of this variability. LimitationsOnly mean or median bile acid concentrations in study cohorts were extracted from studies and compared since bile acid concentrations are rarely reported in individual subjects. Analysing mean or median bile acid concentrations in study cohorts may not give a true sense of bile acid concentrations and therefore their determinants. DiscussionExperimental, analytical and biological sources of mean peripheral bile acid concentration variability were identified. These must be standardised across future studies to clarify the potential of peripheral bile acids as biomarkers.