123 BIOELECTRICAL IMPEDANCE ANALYSIS (BIA) IN THE ASSESSMENT OF BODY COMPOSITION: STANDARDISATION, VALIDISATION AND NORMAL CENTILES FOR BIA-DERIVED LEAN BODY MASS (LBM)

Abstract

BIA is a new method for the assessment of body composition. Until now, it has rarely been validated in children. Reliability studies demonstrated a very low intra- and inter-observer variation. In order to investigate the validity of BIA in predicting LBM in comparison to conventional anthropometry, we measured beside whole-body impedance, total body potassium (TBK) by ⁴⁰K whole-body plethysmography, skinfold thickness and arm circumference in 111 normal children aged 4 to 18 years. The resistance index (height²/impedance) proved to be the best single predictor of TBK-derived LBM (R²=0.94). Inclusion of age, height (in boys) and weight (in girls) into linear prediction equations further improved the prediction of LBM (R²=0.97), reducing the mean prediction error to 2.2 kg. Application of BIA in 2800 normal subjects aged 5 to 20 years allowed to construct normal centile curves for BIA-derived LBM in both sexes. LBM was normally distributed, indicating that the well-known skewness of the weight distribution in normal children is due to an uneven distribution of the fat mass. We conclude that BIA is a fast, non-invasive, accurate and reliable technique to estimate body composition in children.

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