Tubular maximum phosphate reabsorption capacity in living kidney donors is independently associated with one-year recipient GFR

Abstract

The donor glomerular filtration rate (GFR) measured before kidney donation is a strong determinant of recipient graft outcome. No tubular function markers have been identified that can similarly be used in donors to predict recipient outcomes. In the present study we investigated whether the pre-donation tubular maximum reabsorption capacity of phosphate (TmP-GFR), which may be considered a functional tubular marker in healthy kidney donors, is associated with recipient GFR at 1 yr after transplantation, a key determinant of long-term outcome. We calculated the pre-donation TmP-GFR from serum and 24-h urine phosphate and creatinine levels in 165 kidney donors, and recipient125I-iothalamate GFR and eGFR (CKD-EPI) at 12 mo after transplantation. Kidney donors were 51 ± 10 yr old, 47% were men, and mean GFR was 118 ± 26 ml/min. The donor TmP-GFR was associated with recipient GFR 12 mo after transplantation (GFR 6.0 ml/min lower per 1 mg/dl decrement of TmP-GFR), which persisted after multivariable adjustment for donor age, sex, pre-donation GFR, and blood pressure and other potential confounders. Results were highly similar when eGFR at 12 mo was taken as the outcome. Tubular damage markers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin were low and not associated with recipient GFR. A lower donor TmP-GFR before donation, which may be considered to represent a functional measure of tubular phosphate reabsorption capacity, is independently associated with a lower recipient GFR 1 yr after transplantation. These data are the first to link donor tubular phosphate reabsorption with recipient GFR post-transplantation.