Two time-point assessment of bile acid kinetics in humans using stable isotopes

The stable isotope dilution measurement of bile acid pool sizes and turnover rates in humans has involved the collection of nine blood samples over four days. This precludes widespread application to larger population studies. This study describes a two time-point approach for blood sampling without loss of statistical power. Isotopic decay curves of cholic acid, chenodeoxycholic acid and deoxycholic acid acquired in three recent human studies were analysed. The optimal combination of two time-points was determined. Time-points around 12 and 72h after administration allowed for the most accurate description of the decay curves and prediction of kinetic parameters. Analyses of 39 statistical comparisons of kinetic parameters based upon the two time-points and all time-points approaches exhibited only one slightly discrepant result. In conclusion, for group comparison of bile acid kinetics in humans, a two time-point blood collection approach at time-points near 12 and 72h provides statistically reliable data.