Effect of gender and lean body mass on kidney size in healthy 10-year-old children.

When evaluating renal abnormalities, kidney volume is an important parameter. Most reference materials on kidney size in children are based on data from pediatric patients examined for non-uronephrological problems. Renal size is traditionally related to body height, weight, or surface area, but not to body composition. As part of a prospective cohort study we have examined 102 healthy 10-year-old children measuring kidney volume by ultrasonography, body composition by dual energy X-ray absorptiometry, and body height and weight. Boys had significantly larger kidneys than girls. The strongest predictor of kidney volume was lean body mass, overruling height, weight, and surface area. When total kidney volume was related to lean body mass as a ratio, the gender difference in kidney size was no longer significant. A strong negative correlation was found between fat body mass and kidney volume. In conclusion, the strongest predictor of kidney volume in healthy 10-year-old children is lean body mass. The correlation is likely to reflect an association between metabolic active tissue, renal solute load, and kidney volume. We have currently no explanation for the negative correlation between fat body mass and kidney volume.