title: Single FGF-23 measurement and time-averaged plasma phosphate levels in hemodialysis patients.
abstract: OBJECTIVE
  Plasma phosphate levels display considerable intraindividual variability. The phosphatonin fibroblast growth factor 23 is a central regulator of plasma phosphate levels, and it has been postulated to be a more stable marker than conventional CKD-mineral and bone disorder parameters. Thus, fibroblast growth factor 23 has been hypothesized to reflect time-averaged plasma phosphate levels in CKD patients.
  
  
  METHODS
  Among 40 patients from the outpatient dialysis center, serial measurements of plasma calcium and phosphate (before every dialysis session) as well as C-terminal fibroblast growth factor 23, parathyroid hormone, and alkaline phosphatase (one time weekly) were performed over a study period of 4 weeks in November and December of 2011. Intraindividual variability of repeated plasma fibroblast growth factor 23 measurements compared with other CKD-mineral and bone disorder markers was tested, and the association of a single plasma fibroblast growth factor 23 measurement with time-averaged plasma phosphate levels was analyzed.
  
  
  RESULTS
  Against expectations, intraindividual variability of fibroblast growth factor 23 (median coefficient of variation=27%; interquartile range=20-35) was not lower than variability of plasma phosphate (median coefficient of variation=15%; interquartile range=10-20), parathyroid hormone (median coefficient of variation=24%; interquartile range=15-39), plasma calcium (median coefficient of variation=3%; interquartile range=2-4), or alkaline phosphatase (median coefficient of variation=5%; interquartile range=3-10). Moreover, the correlation between the last fibroblast growth factor 23 measurement after 4 weeks and time-averaged plasma phosphate did not surpass the correlation between the last fibroblast growth factor 23 measurement and a single plasma phosphate value (r=0.67, P<0.001; r=0.76, P<0.001, respectively).
  
  
  CONCLUSIONS
  Surprisingly, fibroblast growth factor 23 was not more closely associated to time-averaged plasma phosphate levels than a single plasma phosphate value, and it did not show a lower intraindividual variability than other tested markers of CKD-mineral and bone disorder. Thus, fibroblast growth factor 23 should not be used in clinical practice as a reflector of time-averaged plasma phosphate levels.
authors.affiliation: Department for Internal Medicine IV-Nephrology and Hypertension, Saarland University Medical Center, Homburg, Germany, †Psychological Institute, Humboldt-Universität zu Berlin, Berlin, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Seiler
authors.forename: Gaetano
authors.initials: G
authors.lastname: Lucisano
authors.forename: Philipp
authors.initials: P
authors.lastname: Ege
authors.forename: Lisa H
authors.initials: LH
authors.lastname: Fell
authors.forename: Kyrill S
authors.initials: KS
authors.lastname: Rogacev
authors.forename: Anne
authors.initials: A
authors.lastname: Lerner-Gräber
authors.forename: Matthias
authors.initials: M
authors.lastname: Klingele
authors.forename: Matthias
authors.initials: M
authors.lastname: Ziegler
authors.forename: Danilo
authors.initials: D
authors.lastname: Fliser
authors.forename: Gunnar H
authors.initials: GH
authors.lastname: Heine
mesh_terms: D000368:Aged; D002118:Calcium / Q000097:blood; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood*; D006435:Renal Dialysis
chemical_list: C000717427:FGF23 protein, human; D010281:Parathyroid Hormone; D010710:Phosphates; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D002118:Calcium