FGF23 and secondary hyperparathyroidism: A prospective study measured markers of mineral and bone metabolism among 182 kidney donors and 173 paired controls after kidney donation.20 Donors had evidence of secondary hyperparathyroidism due to a reduction of serum 1,25(OH)2D with significantly higher serum intact parathyroid hormone and fibroblast growth factor 23 concentrations and significantly lower serum 1,25(OH)2D and inorganic phosphate concentrations, measured GFR, and reduced tubular reabsorption of phosphate 6 and 36 months after donation compared with healthy controls.