FGF23 and vitamin deficiency: Total FGF23 was associated with serum phosphate, 25-hydroxyvitamin D3 (25(OH)D), transferrin saturation, and iFGF23.<h4>Conclusion</h4>Elevated sclerostin, total FGF23, and AP concentrations in combination with reduced serum phosphate and (1,25(OH)<sub>2</sub>D<sub>3</sub>) as well as vitamin deficiency or insufficiency were the earliest marker for CKD-MBD in this pediatric population and were present in CKD stage 2.