Stability of Fibroblast Growth Factor 23 in Human Plasma

Abstract

Background: Given the important emerging field of fibroblast growth factor 23 (FGF23) biology, there is a growing need for reliable data on FGF23 assay characteristics. We therefore evaluated the effects of different processing and storage conditions on FGF23 stability, as well as the assay precision of FGF23 measurements using 2 commercially available FGF23 ELISA kits. Methods: We measured plasma concentrations of intact FGF23 (iFGF23) and C-terminal FGF23 (cFGF23) in duplicate in 12 patients with a wide range of kidney function. We used blinded replicate samples to calculate the interassay CV for both assays. We processed the samples immediately after collection, after 6 h at 22°C, or after 24 h at 4°C. We also exposed samples to 0, 1, 2, or 3 freeze-thaw cycles. Results: The interassay CVs for iFGF23 and cFGF23 were 5.2% and 7.2%, respectively. Delayed processing for either 6 h at 22°C or 24 h at 4°C had no significant effect on either iFGF23 or cFGF23, although a nonsignificant trend toward decreased iFGF23 concentrations was observed compared with immediate processing (23% relative decline in concentrations under both delayed processing conditions). Three freeze-thaw cycles had no effect on either iFGF23 or cFGF23 concentrations. Conclusions: FGF23 measurements in human plasma are stable with delayed processing or after undergoing multiple freeze-thaw cycles.

Fibroblast growth factor 23: are we ready to use it in clinical practice?

“…This confirmed two earlier studies that showed 23% reduction of FGF23 measured after a 8 h delay of centrifugation (compared with prompt centrifugation) using the second generation Immutopics assay [21]. Comparable reductions were found with the Millipore and Kainos assays [21,26]. With the DiaSorin assay no such decrease in FGF23 concentrations was found [27].…”

Biological variation of intact fibroblast growth factor 23 measured on a fully automated chemiluminescent platform

“…Reference change value (RCV) and index of individuality (II) (based on the CV I and CV G , without considering the CV A ) were calculated. RCV was calculated by the formula 2 1/2 × 1.96 × (CV A 2 + CV I 2 ) 1/2 with the assumption of two-tailed probability. We added the calculation of the lognormal RCV for decreases and lognormal RCV for increases according to Fokkema et al.…”

“…Some significant papers have described preanalytics, analytical performance of available methods including iFGF23 and biological variation. 2–10 The biological variation of iFGF23 and cFGF23 can differ due to both biological (molecular distinctions, different half-lives) and analytical (different specificities of detection antibodies, different detection systems) factors. Data published previously have described the biological variation of cFGF23 or iFGF23 measured by ELISA.…”

Fibroblast Growth Factor 23 Associates with Death in Critically Ill Patients

“…Interassay coefficients of variation for cFGF23 and iFGF23, determined from blinded replicate samples, were ,10%. We report additional performance characteristics for the cFGF23 and iFGF23 assays elsewhere (17).…”