Blood calcium and phosphate were measured weekly ; iPTH , 25 ( OH ) D , 1,25-dihydroxyvitamin D3 ( 1,25 [ OH ] 2D ) , and bone turnover markers , trimonthly ; fetuin A and fibroblast growth factor 23 ( FGF-23 ) serum levels and aortic calcification scores were determined at weeks 0 and39 .