Pre-analytical stability of FGF23 with the contemporary immunoassays

Background: Several publications have reported on the pre-analytical stability of fibroblast growth factor 23 (FGF23) and some recommend coating blood collecting tubes with protease inhibitors, in order to prevent degradation. These recommendations are based on observations for a first generation assay for the measurement of intact FGF23. However, if this also applies for the contemporary immunoassays, and at what stage of pre analysis, is unknown. Methods: We reviewed data from these previous reports on the issue of FGF23 stability and complemented these findings with data from novel experiments. Results: We concluded that the contemporary intact FGF23 assays by Immutopics, Kainos, Millipore and DiaSorin do not suffer from immediate loss of FGF23 signal and do not require blood withdrawal in protease inhibitor-coated collecting tubes. Nevertheless, FGF23 concentrations do decline when centrifugation is delayed up to 8 h and prompt centrifugation is therefore advised.