Glomerular filtration rate (GFR) declines with aging however most data are obtained from subjects younger than 65years, questioning the validity of normal GFR range for older individuals. Age of candidates for living kidney donation is increasing worldwide and lack of GFR references for older donors complicates the selection process.

In this retrospective, observational, multi-center study, percentiles of mGFR in effective kidney donors (EKD) were calculated from a development cohort of French and Belgian kidney donors younger than 65years (n=1983). From the French kidney donor study, 147 EKD older than 65years were considered as the internal validation cohort. In an external validation cohort, data from six centers were included on mGFR of subjects older than 65years, either EKD or healthy persons (HP) from the general population (Germany, Sweden, Norway, Netherlands, France, n=329). Percentiles were derived for the development database, using quantiles modeled as cubic splines with two linear parts joining at one age-knot of 40years. We calculated the percentage of results from the internal and external validation cohorts that were within the extrapolated percentile 5th (P5) and percentile 95th (P95).

Individuals in the development cohort were younger than individuals in the internal or external validation cohort (47.3±10.5years vs. 68.8±2.9years or 71.4±6.4years; P<0.001). Among the 147 EKD 135 (91.2%) of subjects were between P5-P95 (Fig. 1). Considering the whole external validation cohort (n=329), 5 subjects had mGFR lower than extrapolated P5 (1.5%), 25 were above P95, leaving 299 (90.9%) with mGFR between P5 and the extrapolated P95.

Extrapolated mGFR percentiles fit well with the distribution of mGFR in individuals older than 65. Extrapolation of percentiles to individuals older than 65 is useful to define normal mGFR for age. Clinically, those percentiles may be helpful for the selection of candidates to living kidney donation.