Uric acid and IGF1 as possible determinants of FGF23 metabolism in children with normal renal function

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone and a suppressor of renal 1 alpha hydroxylase. Although circulating values of FGF23 are increased in early chronic kidney disease (CKD), the interplay between FGF23 levels, growth and nutritional biomarkers has not been evaluated in children with normal renal function. We performed a secondary analysis of the cross-sectional observational INU23 study in 98 children (51 boys, mean age 10.5 +/- A 3.9 years) with preserved renal function (glomerular filtration rate (GFR) 114 +/- A 14 ml/min/1.73 m(2)). In bivariate analyses, C-terminal FGF23 levels were positively related to phosphorus and uric acid levels. Intact FGF23 levels were positively associated with uric acid and insulin growth factor 1 (IGF1) levels, with similar results for age, body mass index (BMI), and 25OH vitamin D (25(OH)D). By multivariable analyses, 25(OH)D, uric acid, and phosphorus were independent predictors of C-terminal FGF23, while 25(OH)D, uric acid, and IGF1 were independent predictors of intact FGF23. In children with preserved kidney function, the association between FGF23, uric acid, and IGF1 suggests that FGF23 could be an early nutritional indicator of high protein and phosphate intake. The association between FGF23 and IGF1 also suggests a relationship between FGF23 and growth, and warrants further investigation.