Determination of fibroblast growth factor 23.
BACKGROUND
Fibroblast growth factor 23 (FGF-23) is a recently discovered hormone, which plays a key role in phosphate regulation. To investigate whether FGF-23 can be determined reliably, we validated the three available FGF-23 assays.


METHODS
Currently, two intact FGF-23 assays (Kainos; Immutopics) and one C-terminal FGF-23 assay (Immutopics) are available. We determined intra- and inter-assay variation, linearity and matrix interference in these assays. Moreover, we compared assay results from healthy subjects with those of patient groups with expected high FGF-23 concentrations.


RESULTS
Intra-assay variation was reasonably good in all three assays. Inter-assay variation and linearity were poor for the intact Immutopics assay but reasonable for both other assays. Immutopics assays gave best results in ethylenediaminetetraacetic acid (EDTA) plasma, while the Kainos assay showed comparable reproducibility in EDTA plasma and serum. Although the manual of the Kainos assay states that an automatic washing machine can be used, acceptable results were only found by manual washing. Patients with kidney disease and patients with hypophosphatemic osteomalacia had increased C-terminal FGF-23 concentrations compared with healthy controls.


CONCLUSIONS
Two assays of reasonable quality are available for FGF-23, the intact FGF-23 assay (Kainos) provided proper attention is paid to the washing procedure, and the C-terminal assay (Immutopics).
Heijboer
Annemieke C
AC
Department of Clinical Chemistry, VU University Medical Center, 1081 HV Amsterdam, The Netherlands. a.heijboer@vumc.nl
Levitus
Marieke
M
Vervloet
Marc G
MG
Lips
Paul
P
ter Wee
Piet M
PM
Dijstelbloem
Hilde M
HM
Blankenstein
Marinus A
MA
D001681:Biological Assay / Q000379:methods*; D004797:Enzyme-Linked Immunosorbent Assay; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000032:analysis*; D006801:Humans; D015203:Reproducibility of Results
C000717427:FGF23 protein, human; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23