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

Author(s): Smith ER, McMahon LP, Holt SG

Publication: Clin Chem Lab Med, 2013, Vol. 51, Page 1971-81

PubMed ID: 23729624 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   The purpose of this study was to determine the effects of delayed centrifugation, tube type, assay manufacturer and targeting intact rather than c-terminal protein on measured levels of FGF23 in plasma and serum from healthy individuals and those on hemodialysis therapy. For stability studies, blood was collected into plain tubes and P100 tubes, but for all other comparisons, blood was collected into P100 or serum gel tubes.

   Summary of Findings:

   iFGF23 concentrations declined when whole blood was stored for 8 h in plain tubes before centrifugation rather than being centrifuged immediately, but the difference was smaller when assayed using the Millipore (7%, p=0.0001) or Kainos (5%, p=0.016) kits than the Immunotopics kit (23%, p=0.001), and there was no effect on cFGF23 levels. Further, delayed centrifugation of specimens in P100 tubes did not impact iFGF23 levels. Mean FGF23 was slightly higher in plasma than serum as measured by the Kainos kit (43.8 vs 40.2, p=0.015). The Millipore iFGF23 assay showed smaller changes in absorbance with increasing FGF23 concentrations resulting in lower sensitivity than the Kainos and Immunotopics iFGF23 assays. The concentration of endogenous FGF23 was higher when measured using the Kainos kit than the Immunotopics or Millipore kits, and this disparity increased with increasing FGF23 concentration such as those found in the patients undergoing hemodialysis therapy. When plasma was spiked with FGF23, the Immuntopics kit measured higher levels than expected when spiked with 260 pg/mL, but was accurate at 20 pg/mL and 80 pg/mL. In contrast, the Millipore and Kainos kits measured lower levels of FGF23 than expected at all concentrations, with a larger underestimation at 260 pg/mL. FGF23 levels determined using the Immunotopics cFGF23 assay were not significantly correlated with levels determined using any of the three iFGF23 assays.

   Biospecimens

   • Bodily Fluid - Blood
   • Bodily Fluid - Serum
   • Bodily Fluid - Plasma

   Preservative Types

   • Frozen

   Diagnoses:

   • Normal
   • Other diagnoses

   Platform:

   Analyte	Technology Platform
   Protein	ELISA

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Biospecimen Aliquots and Components	Biospecimen components	20 pg/mL 80 pg/mL 260 pg/mL
   Storage	Storage duration	0 h 8 h
   ELISA Specific	Technology platform	Millipore iFGF23 Kainos iFGF23 Immunotopics iFGF23 Immunotopics cFGF23
   Preaquisition	Diagnosis/ patient condition	Undergoing chronic hemodialysis therapy
   Storage	Type of storage container	P100 tube Plain tube
   Biospecimen Aliquots and Components	Blood and blood products	Plasma Serum
   Biospecimen Aliquots and Components	Centrifugation	Centrifugation delays investigated
   Biospecimen Acquisition	Type of collection container/solution	Plain tube P100 tube

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