Single FGF-23 Measurement and Time-Averaged Plasma Phosphate Levels in Hemodialysis Patients

• Published in: Clinical journal of the American Society of Nephrology Vol. 8; no. 10; pp. 1764 - 1772
• Main Authors: Seiler, Sarah, Lucisano, Gaetano, Ege, Philipp, Fell, Lisa H, Rogacev, Kyrill S, Lerner-Gräber, Anne, Klingele, Matthias, Ziegler, Matthias, Fliser, Danilo, Heine, Gunnar H
• Format: Journal Article
• Language: English
• Published: United States American Society of Nephrology 07-10-2013
• Subjects: Aged; Calcium - blood; Female; Fibroblast Growth Factors - blood; Humans; Kidney Failure, Chronic - blood; Male; Middle Aged; Original; Parathyroid Hormone - blood; Phosphates - blood; Renal Dialysis
• ISSN: 1555-9041; 1555-905X
• DOI: 10.2215/CJN.13021212

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.
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.
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).
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.