title: C-Terminal to Intact Fibroblast Growth Factor 23 Ratio in Relation to Estimated Glomerular Filtration Rate in Elderly Population.
abstract: OBJECTIVE
  An analytical equivalence between intact fibroblasts growth factor(iFGF23) and C-terminal(cFGF23) assays is logically expected, however, numerous studies demonstrate lack of a strong association between them. Previously, we have demonstrated the increase in cFGF23 slightly precedes the increase of iFGF23 with the impairment of kidney excretory function; without actually analyzing the ratio between both assays, which are postulated to be affected by declining kidney function. Therefore, the aim of this study was to analyze the ratio between C and iFGF23 in relation to the estimated glomerular filtration rate (eGFR) in an elderly population.
  
  
  METHODS
  We analysed the variability of c/iFGF23 ratio in the population of 3264 elderly PolSenior study participants (≥ 65years) in the relation to eGFR calculated according full Modification of Diet in Renal Disease, serum levels of C-reactive protein (hs-CRP), and iron.
  
  
  RESULTS
  The log10(c/i FGF23 ratio) increased in the subsequent CKD stages. Serum iron and CRP levels reduced the log10 and increased it with age in multivariate regression analysis.
  
  
  CONCLUSIONS
  Our results suggest impairment in the cleavage of the C-terminal FGF23 fragments with the deterioration of kidney excretory function and age in the elderly population. Inflammation and low serum iron level seems to diminish degradation capacity of FGF23 fragments.
authors.affiliation: Pathophysiology Unit, Department of Pathophysiology, Faculty of Medicine in Katowice, Medical University of Silesia in Katowice, Katowice, Poland.
authors.forename: Maria
authors.initials: M
authors.lastname: Bożentowicz-Wikarek
authors.forename: Aleksander
authors.initials: A
authors.lastname: Owczarek
authors.forename: Piotr
authors.initials: P
authors.lastname: Kocełak
authors.forename: Magdalena
authors.initials: M
authors.lastname: Olszanecka-Glinianowicz
authors.forename: Andrzej
authors.initials: A
authors.lastname: Więcek
authors.forename: Jerzy
authors.initials: J
authors.lastname: Chudek
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000032:analysis*; D005919:Glomerular Filtration Rate; D006801:Humans; D007249:Inflammation / Q000503:physiopathology; D007501:Iron / Q000097:blood; D000090463:Iron Deficiencies; D010446:Peptide Fragments / Q000032:analysis*
chemical_list: C000717427:FGF23 protein, human; D010446:Peptide Fragments; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D007501:Iron