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Licensed Unlicensed Requires Authentication Published by De Gruyter May 24, 2013

Method-specific differences in plasma fibroblast growth factor 23 measurement using four commercial ELISAs

Edward R. Smith, Lawrence P. McMahon and Stephen G. Holt

Abstract

Background: There is growing interest in measuring plasma fibroblast growth factor 23 (FGF23) concentration in a number of clinical settings. However, data comparing current commercial intact and C-terminal FGF23 assays is lacking.

Methods: We used plasma samples collected from a cohort of healthy adults and patients undergoing chronic haemodialysis therapy (n=67) to compare the precision, recovery, linearity and pre-analytical stability characteristics of four commercial FGF23 assays from Kainos, Millipore and Immutopics Inc. Method agreement was evaluated using Passing-Bablok regression and difference plot analysis.

Results: Both Millipore and Immutopics intact FGF23 kits demonstrated marked negative proportional bias relative to Kainos assay readout, particularly in the haemodialysis group, and poor recovery of purified FGF23 standard at high spiking concentrations. Dilution of high-reading samples with saline as recommended by the Immutopics kit resulted in significant deviation from linearity. Immutopics C-terminal FGF23 concentrations displayed a strong association with intact FGF23 concentrations determined with all three intact assays in the haemodialysis group, but showed no significant correlation within the physiological range. Only intact FGF23 measurements made with the Immutopics assay demonstrated evidence of significant instability 8 h after venepuncture.

Conclusions: Current ELISA kits for plasma intact FGF23 measurement show poor analytical agreement, and cannot be used interchangeably. This is mainly due to differences in calibration. Harmonisation of available assays using a common international standard would facilitate more meaningful interpretation of data from studies using different kits. Discordance between intact and C-terminal FGF23 assay measurements is more marked at physiological concentrations than in patients undergoing haemodialysis.


Corresponding author: Edward R. Smith, Department of Renal Medicine, Eastern Health Clinical School, Faculty of Medicine Nursing and Health Sciences, Monash University, Level 2, 5 Arnold Street, Box Hill, Victoria 3128, Australia, Phone: +61 03 98996810, Fax: +61 3 98996810, E-mail:

We thank Dr. Michael MX Cai (Eastern Health, Box Hill) for assisting with patient recruitment and procurement of samples for this study.

Conflict of interest statement

Authors conflict of interest disclosure: The authors stated that there are no conflicts of interest regarding the publication of this article. Research funding played no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication.

Research funding: This work was partly funded by an unrestricted investigator-initiated research grant from Amgen Australia Pty Ltd and financial assistance from Eastern Health and Monash University.

Employment or leadership: None declared.

Honorarium: ERS has received honoraria from Shire; SGH has received honoraria from Amgen, Baxter and Shire.

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Received: 2013-03-18
Accepted: 2013-04-28
Published Online: 2013-05-24
Published in Print: 2013-10-01

©2013 by Walter de Gruyter Berlin Boston