Evaluation of a method for fibroblast growth factor-23: a novel biomarker of adverse outcomes in patients with renal disease.
Abstract Background: Fibroblast growth factor 23 (FGF-23), a phosphaturic peptide hormone secreted by the osteoblasts, is an important regulator of phosphorus and vitamin D metabolism. In chronic kidney disease, FGF-23 levels rise with declining kidney function. Increasing FGF-23 levels are associated with increasing risk of mortality in dialysis patients. Two assays for FGF-23 have been reported. One assay detects only full-length/intact FGF-23. In contrast, the carboxy-terminal assay recognizes both intact and carboxy-terminal FGF-23.


OBJECTIVE
The aim of this study was to evaluate both assays for FGF-23. Test samples were analyzed with both the intact and carboxy-terminal FGF-23 enzyme-linked immunosorbent assay (ELISA) kits according to manufacturers' instructions.


RESULTS
Carboxy-terminal FGF-23 showed very good precision with coefficients of variation (CV) ranging from 4% to 10.5%, whereas the CVs for intact FGF-23 were not very good (6-37.5%). The carboxy-terminal assay was linear, stable in plasma samples, and was not affected by common interferents. Also, the carboxy-terminal FGF-23 assay appeared to correlate better with worsening of kidney function as assessed by plasma creatinine and calculated estimated glomerular filtration rate (eGFR).


CONCLUSIONS
Thus, the carboxy-terminal FGF-23 assay is robust and can be used in prospective trials to validate its utility as a biomarker of adverse outcomes in patients with renal disease.
Devaraj
Sridevi
S
Laboratory for Atherosclerosis and Metabolic Research, University of California Davis Medical Center, Sacramento, California 95817, USA
Duncan-Staley
Catherine
C
Jialal
Ishwarlal
I
D015415:Biomarkers / Q000032:analysis / Q000097:blood; D003404:Creatinine / Q000032:analysis / Q000097:blood; D003429:Cross Reactions; D018450:Disease Progression; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000032:analysis* / Q000097:blood / Q000737:chemistry; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D007674:Kidney Diseases / Q000097:blood / Q000175:diagnosis* / Q000473:pathology; D011379:Prognosis; D020033:Protein Isoforms / Q000032:analysis / Q000097:blood; D017434:Protein Structure, Tertiary / Q000502:physiology
D015415:Biomarkers; C000717427:FGF23 protein, human; D020033:Protein Isoforms; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D003404:Creatinine