A prospective study of fibroblast growth factor-23 in children with chronic kidney disease.

BACKGROUND: Fibroblast growth factor-23 (FGF-23) is a novel regulator of phosphate metabolism; however, the clinical knowledge is limited in children with chronic kidney disease (CKD) who are at risk of developing mineral bone disorder. METHODS: This prospective study over 2 years investigated the development of bone mass and bone turnover in relation to serum FGF-23 in children with CKD. Thirteen patients, 4-15 years, were included with a median corrected glomerular filtration rate (GFR) of 38 (range 7-74) mL/min/1.73 m(2). RESULTS: Median FGF-23 was 127 RU/mL at baseline and 70 RU/mL at follow-up. Five patients had FGF-23 levels exceeding the upper reference limit of 141 RU/mL for healthy children. No correlation with age or puberty was found. FGF-23 was inversely correlated with GFR, r = -0.73 (p <0.05). Four of the five patients within CKD stages 4-5 (GFR <30 mL/min/1.73 m(2)) had elevated FGF-23 levels and two patients with end-stage renal disease had markedly high levels of FGF-23 (1333 and 1700 RU/mL). One of these patients was transplanted after 1 year, which normalized FGF-23 to 70 RU/mL at follow-up. FGF-23 was significantly associated with PTH, r = 0.69 (p <0.01). FGF-23 correlated with osteocalcin, but not with other markers of bone turnover. Total body bone mineral density (BMD) was not correlated with FGF-23, however, the lumber spine BMD Z-score correlated with FGF-23 at baseline, r = 0.61 (p <0.05). CONCLUSIONS: Although a small study group, this prospective study suggests that FGF-23 is associated with GFR, PTH, and lumbar spine BMD in pediatric patients with various degrees of CKD.