Normal values of the bioelectrical impedance vector in childhood and puberty

The purpose of this study was to determine the reference, bivariate, and to lerance intervals of the whole-body impedance vector in Italian children. T his was a cross-sectional, multicenter study, and participants were chosen from the general school population. The impedance vector (standard, tetrapo lar analysis at 50-kHz frequency) was measured in 3110 subjects, ages 2 to 15 y, and 2044 healthy children (1014 male and 1030 female) with weight and height within the 95th percentile were selected for the analysis (resistan ce-reactance graph method). The age-specific 95% confidence intervals of me an vectors and the 95%, 75%, and 50% tolerance intervals for individual vec tor measurements were plotted using resistance and reactance components sta ndardized by the subject's height. Mean vectors from both sexes with separa te 95% confidence ellipses were considered as representative of eight diffe rent age groups, from 2 to 13 y. There was a statistically significant sex effect on vector distribution from boys and girls in the age group of 13 to 15 y. The impedance vector distribution of children was also compared with healthy adult subjects (354 male and 372 female, age 15 to 85 y). There wa s a progressive, statistically significant vector shortening from age 2 to 15 y toward the adults' vector position. In conclusion, we established the trajectory followed by the mean impedance vector in children over ages 2 to 15 y and also obtained the reference, bivariate, and 95%, 75%, and 50% tol erance intervals of the impedance vector by age for healthy children, with which the vectors from children with altered body composition can be tested . Nutrition 2000;16:417-424. (C)Elsevier Science Inc. 2000.