Effects of aging on glomerular function and number in living kidney donors

To elucidate the pathophysiologic changes in the kidney due to aging, we used physiological, morphometric, and imaging techniques to quantify GFR and its determinants in a group of 24 older (≥55 years) compared to 33 younger (≤45 years) living donors. Mathematical modeling was used to estimate the glomerular filtration coefficients for the whole kidney (K_f) and for single nephrons (SNK_f), as well as the number of filtering glomeruli (N_FG). Compared to younger donors, older donors had a modest (15%) but significant depression of pre-donation GFR. Mean whole-kidney K_f, renocortical volume, and derived N_FG were also significantly decreased in older donors. In contrast, glomerular structure and SNK f were not different in older and younger donors. Derived N_FG in the bottom quartile of older donors was less than 27% of median-derived N_FG in the two kidneys of younger donors. Nevertheless, the remaining kidney of older donors exhibited adaptive hyperfiltration and renocortical hypertrophy post-donation, comparable to that of younger donors. Thus, our study found the decline of GFR in older donors is due to a reduction in K_f attributable to glomerulopenia. We recommend careful monitoring for and control of post-donation comorbidities that could exacerbate glomerular loss.