Sonographic measurement of absolute and relative renal length in adults

The aim of this study was to evaluate sonographically measured absolute and relative lengths of normal kidneys according to subject height, sex, and age.

Real-time sonography was performed on 202 subjects. Measurements of longitudinal renal diameter represented absolute renal length. Relative renal length was calculated using the kidney length: body height ratio (KBR).

Statistical analyses were done on findings in 175 subjects without renal impairment (104 men and 71 women) whose ages ranged from 17 to 85 years (mean +/- SD, 46.3 +/- 17.1). The mean heights of the subjects were 176 +/- 7 cm for men and 167 +/- 6 cm for women. The left kidney was absolutely (mean +/-SD, 112 +/- 9 mm) and relatively (mean KBR +/- SD, 0.655 +/- 0.042) longer than the right kidney (absolute length, 110 +/- 8 mm; KBR, 0.641 +/- 0.038), regardless of sex (p < 0.01). The absolute renal length was significantly greater in men than in women for both kidneys (p < 0.01), but there was no significant difference between KBRs (p > 0.05). Renal length decreased with age, and the rate of decrease seemed to accelerate at 60 years and older. When height and age were included in the multivariate regression analysis, sex was not a significant predictor of kidney length.

Relative renal length better represents kidney size than absolute renal length because it eliminates sex and height differences.