Validation of laboratory methods to measure biomarkers of mineral metabolism

This project confirmed acceptable performance of the new-generation intact FGF-23 assay (Immutopics, Inc) and the Fetuin A assay (Epitope Diagnostics, Inc; within- and between-batch precision CVs <20%, linearity r2>0.99).  We established that the discrepancy in results between our previous FGF-23 stability studies and published reports was due to differences in sample handling during the experiments.  Our approach of using separate vacutainers that were only opened at the particular time-point (as in samples collected for a randomised controlled trial) resulted in <5% change in plasma FGF-23 concentration following a delay in processing of up to 6 hours at room temperature or 24 hours chilled, compared with >17% change for repeat sampling from one vacutainer.  Plasma concentrations of Fetuin A changed by <3.5% in chilled samples up to 24 hours, but exhibited greater variability at room temperature.  We conclude that both analytes could be measured reliably in samples from HPS and SHARP.