FGF23 and Abnormal renal physiology: On the other hand, recent studies suggested an increase in C-terminal FGF23 may precede an increase in intact FGF23 in the relatively early phase of CKD [39] and that cleavage of FGF23 might be a major determinant for FGF23 activity in various diseases [40,41,42]; therefore, serum levels of intact FGF23 should be assessed, especially among populations including patients without severe renal dysfunction, such as the current study sample.