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.
Authors' Disclosures or Potential Conflicts of Interest: Upon manuscript submission, all authors completed the author disclosure form.
Employment or Leadership: None declared.
Consultant or Advisory Role: None declared.
Stock Ownership: None declared.
Honoraria: None declared.
Research Funding: D.E. Leaf, National Institute of Diabetes and Digestive Kidney Diseases (K23DK106448), UAB-UCSD O'Brien Center for Acute Kidney Injury Research (NIH P30-DK079337) to the institution; S.M. Vaingankar, National Institute of Diabetes and Digestive Kidney Diseases (R01DK094894), and the National Heart, Lung, and Blood Institute (R01HL108629); S.S. Waikar, National Institute of Diabetes and Digestive Kidney Diseases (R01DK093574, R01DK103784, U01DK104308, and U01DK085660).
Expert Testimony: None declared.
Patents: None declared.
Role of Sponsor: No sponsor was declared.
- Received October 28, 2016.
- Accepted January 30, 2017.
- © 2017 American Association for Clinical Chemistry