Background: This report describes preliminary results of a study of glomerular number and volume and their associations, in kidneys of people coming to autopsy.
Methods: Both kidneys were weighed at autopsy and the right kidney was perfusion-fixed and sub-sampled for stereological estimation of total glomerular number, and of mean renal corpuscle volume, using the physical disector/fractionator combination.
Results: The 78 kidneys studied so far were from Australian Aborigines, Australian non-Aborigines, US blacks and US whites, ages newborn to 84 years. Glomerular number ranged almost ninefold (from 210,332 to 1,825,380), with mean (SD) of 784,909 (314,686); it decreased throughout adult life (r=-0.32, P=0.009). Mean renal corpuscle volume varied 5.6-fold in adults and was inversely correlated with glomerular number (r=-0.38, P=0.001). Total renal corpuscle volume varied in adults by a factor of 15.8. Kidney weight correlated with body surface area (BSA) at all ages (r=0.76, P < 0.001); it varied 3.4-fold among adults, while kidney weight/m2 varied 3.7-fold. The percentage of sclerosed glomeruli varied from 0 to 23%, and it correlated strongly with age (r=0.58, P < 0.001). Females had smaller kidneys than males, and, marginally, fewer glomeruli. There were no significant variations by ethnic group.
Conclusions: These extraordinary ranges of glomerular number and size among ostensibly "normal" people, and their inverse relationship, probably have important implications for susceptibility to renal insufficiency. People with low glomerular (nephron) numbers are likely to be particularly predisposed, with the process marked by compensatory hypertrophy of residual nephrons, which, in turn, accelerates their obsolescence. Much, however, remains to be done, including evaluation of history, clinical features, accompanying pathology, detailed renal morphology, and further pursuit of potentially defining characteristics in high risk groups.