Age, kidney function, and risk factors associate differently with cortical and medullary volumes of the kidney

The kidney atrophies in patients with advanced chronic kidney disease (CKD) but factors influencing kidney size in normal adults are less clear. To help define this we measured kidney volumes on contrast-enhanced CT images from 1344 potential kidney donors (ages 18 to 75 years). Cortical volume per body surface area progressively declined in both genders with increased age. Statistically, this was primarily dependent on the age-related decline in glomerular filtration rate (GFR). Independent predictors of increased cortical volume per body surface area were male gender, increased GFR, increased 24-hour urine albumin, current smoker, and decreased high-density lipid cholesterol. Medullary volume per body surface area increased with age in men while it increased with age in women until age 50 followed by a subsequent decline. Independent predictors of increased medullary volume per body surface area were older age, male gender, increased GFR, increased 24-hour urine albumin, increased serum glucose, and decreased serum uric acid. Thus, while cortical volume declines with age along the same biological pathway as the age-related decline in GFR and albuminuria some CKD risk factors are actually associated with increased cortical or medullary volume among relatively healthy adults. Underlying hypertrophy or atrophy of different nephron regions may explain these findings.