Fibroblast growth factor 23 (FGF23) and early chronic kidney disease in the elderly

Background: Better biomarkers of CKD reflecting responses to decreased glomerular filtration rate (GFR) are needed. We determined the value of estimated GFR (eGFR) as a threshold for the increase of plasma cFGF23 (C-terminal) and intact fibroblast growth factor-23 (iFGF23) (intact) concentrations in the course of chronic kidney disease (CKD) and compared this eGFR value with values related to increased serum intact parathyroid hormone (iPTH) or phosphorus concentrations in an elderly population.

Methods: We measured plasma iFGF23, cFGF23, serum phosphorus, calcium, albumin, creatinine, urea, cystatin C, iPTH and vitamin 25-OH-D3 in 3780 population-based study participants aged ≥ 65 years.

Results: Serum phosphorus concentrations hardly increased until mean eGFR reached 47.3 ± 4.7 mL/min/1.73 m(2) but then increased exponentially. Similarly, both iPTH and iFGF23 increased slightly in early CKD but then increased exponentially when eGFR reached 55.0 ± 4.2 mL/min/1.73 m(2) for iPTH and 51.6 ± 5.7 mL/min/1.73 m(2) for iFGF23. The departure point for exponential increases in cFGF23 preceded those for iPTH and iFGF23 and occurred at a mean eGFR of 57.7 ± 7.8 mL/min/1.73 m(2). The prevalence of increased iFGF23 occurred at a remarkably higher eGFR value than that of cFGF23 across the CKD stages.

Conclusions: The increase in cFGF23 preceded both the increase in iPTH and iFGF23 as eGFR declined. Increased plasma iFGF23 level did not precede the rise in serum iPTH concentrations and did not occur before stage-3 CKD in elderly persons. However, cFGF23 was not an early marker of CKD in the elderly subjects.