FGF23 and chronic kidney disease: However, as this study is cross-sectional, we are unable to address temporal relationships; it is neither possible to analyze if increasing levels of serum phosphate, albeit within the normal ranges, in prevalent transplant patients are the primary perturbation leading to FGF-23 elevation, nor if the modulation of this relationship by PTH levels is similar to the pathophysiology of CKD prior to transplantation.