Determination of fibroblast growth factor 23

Abstract

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. Conclusion: 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).

Effects of Dietary Phosphate and Calcium Intake on Fibroblast Growth Factor-23

“…This conclusion is based on the assumption that the C-terminal assay detects cFGF23 and iFGF23, whereas the iFGF23 assay detects only iFGF23 (28). We showed that throughout the day cFGF23 increased, whereas iFGF23 decreased, which suggests accumulation of FGF23 fragments.…”

Fibroblast growth factor is associated to left ventricular mass index, anemia and low values of transferrin saturation

“…But studies in which iFGF-23 (kainos; immutopics) and cFGF-23 (immutopics) measurements are compared are inadequate. In a study intra-assay variation was found to be good in all three assays but in terms of interassay and linearity, kainos iFGF-23 and cFGF-23 assays were found to be better 50 . In another study strong positive correlation was determined between iFGF assays and cFGF assay in the HD patients 51 .…”

Acute Effects of Very-Low-Protein Diet on FGF23 Levels

“…The Kainos Intact FGF23 assay is standardized to measure FGF23 in picograms per milliliter; it has a lower limit of detection of 3 pg/ml and intraassay and interassay coefficients of variation of less than 5%. The FGF23 assays were performed using stored plasma or serum according to the specified kit direction (18)(19)(20). All samples were measured in duplicate after a single thaw, with the mean value used in subsequent analysis.…”