*Purpose: The aim of this study is to investigate whether reduction in glomerular filtration rate (GFR) after kidney donation causes mineral metabolism alterations, and also investigate what factors associated with mineral metabolism adaptation.

*Methods: 144 living kidney donors (LKDs) in Seoul St. Mary’s hospital between May 2016 and September 2018 were enrolled, prospectively. Laboratory evaluation, 24-hour urine collection and Technetium-99m diethylene-triamine-pentaacetate scan were performed in two subsequent time points; pre-donation and 6-month after donation. LKDs were divided into 2 groups according to the difference of fractional excretion of phosphate (FEPi).

*Results: 6-month after uni-nephrectomy, estimated GFR (eGFR) declined (100.76 to 66.89 ml/min/1.73m²) significantly (p<0.001). After donation, serum phosphorus decreased (p<0.001), whereas FEPi (13.34 to 20.23 %, p<0.001) and serum iPTH (38.70 to 52.20 pg/ml, p<0.001) were increased. In subgroup analysis, semi-log FGF-23 tended to increase after donation (85.20 to 106.71 pg/ml, p=0.092). Percentage change in eGFR was significantly higher in high delta FEPi group (p=0.043). In multivariable logistic regression, the odds ratio of percentage change in eGFR was 1.076 (p=0.005).

*Conclusions: After uni-nephrectomy, LKDs develop secondary hyperparathyroidism related to a decreased serum phosphorus, increased FEPi. Moreover, the greater the reduction of GFR occurs, the greater adaptation of mineral metabolism follows.

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