THE AGING KIDNEY

An age-associated decrease in renal mass is common, although most studies done to explore this issue did not exclude individuals with comorbid conditions. Population selection and design type have limited the assessment of renal changes in the elderly, as many have used hospitalized or otherwise institutionalized elders in a cross-sectional design. Interestingly, in elderly patients who suffered traumatic death and in whom renal disease and/or important comorbid conditions were excluded, there was no significant decrease in renal mass. In patients with decreased renal mass, the number of functioning glomeruli decreases with a greater proportion lost in the cortex and relative sparing of medullary glomeruli. Although the number of glomeruli decline, the remaining glomeruli increase in size. Consequently, any injury to remaining nephrons is more consequential. There is an increase in glomerular hyalinization or sclerosis in apparently healthy elderly individuals. Once again, the change in the number of glomeruli varies greatly in elders, although the presence of glomerulosclerosis is indicative of subclinical renal injury from comorbid conditions affecting renal structure.

RENOVASCULAR CHANGES

There is a decrease in glomerular filtration rate (GFR) in elderly patients, although this may occur to a lesser extent in the aging of healthy individuals. Nevertheless, an age-related decline in GFR is an independent predictor of adverse outcomes such as death and cardiovascular disease. Blood flow decreases more than the GFR, leading to an increased filtration fraction and subsequent increase risk of nephron damage.