Bioelectrical impedance vector reference values for assessing body composition in a Spanish child and adolescent population.

Objectives: Reference values of the bioelectrical impedance vector for the Spanish child and adolescent population are needed for assessing body composition and hydration status in this population. The aim of this study is to provide reference values of the bioelectrical impedance vector in Spanish children and adolescents aged 4-18 years from Castilla y León.

Methods: This was a cross-sectional descriptive study conducted in 4401 Spanish healthy children and adolescents aged 4-18 years (2265 boys and 2136 girls). Resistance and reactance were measured with a single-frequency impedance analyzer at 50 kHz (tetrapolar analysis). The values of resistance and reactance normalized by height were used to plot the bivariate 50th, 75th, and 95th percentiles of the population by age group. Mean impedance vectors were compared with Hotelling's T test for vector analysis (differences being considered significant if p < .05).

Results: Tolerance ellipses were drawn for the Spanish child and adolescent population studied. The mean impedance vector showed displacement across all age groups except for (1) girls aged 12-13 years, (2) girls aged 15-18 years, and (3) boys aged 16-18 years. There were sex-related differences in the mean impedance vector in all age ranges, even in prepubertal children. Among adolescents, the patterns of the vector displacement were consistent with the timing of normal growth and development in all groups and are attributable to the maturation process.

Conclusions: New tolerance ellipses have been constructed for Spanish children and adolescents by sex and age. These ellipses reflect the timing of normal childhood growth and development.