The association between serum intact fibroblast growth factor 23 and incident CKD , defined as the new onset of eGFR < 60 ml/min per 1.73 m ( 2 ) that represented a 25 % decrease from baseline in an individual with eGFR60 ml/min per 1.73 m ( 2 ) and no microalbuminuria ( < 30 mg/g creatinine ) at baseline , was tested .