Is kidney length a good predictor of kidney volume?

Kidney length is commonly used to determine kidney size; however, its relationship to kidney volume is not well established. This study evaluated the association between kidney length and kidney volume. Eighteen healthy adults (9 men and 9 women) consented to take part in this prospective study; all 18 underwent spiral computerized tomography (CT) of the kidneys, 14 of 18 also underwent kidney ultrasound. Kidney volume was measured by totaling the areas of the CT scan cuts, and kidney length was measured both on the kidney ultrasound and on the CT scan. Each independent variable, CT length (CTL) and ultrasound length (USL), was regressed against the dependent variable, kidney volume. Kidney length explained only 10% of the variability of the volume, although length x width was a better predictor of kidney volume (r = 0.72, P < 0.001). It was concluded that kidney length does not reliably predict kidney volume and that other methods, both clinical and radiologic, should be considered when a more exact determination of renal volume is clinically relevant.