Predicting fat-free mass in children using bioimpedance analysis

Bioelectric Impedance Analysis (BIA) is a simple, safe and inexpensive method for the body composition assessment both in pediatric and adult samples. The aim of our study was to validate the impedance index, ZI (H²/Z, height in cm²/impedance) as a predictor factor of Fat-free Mass (FFM) in a sample (75) of normal children age (9.9±1.4, yrs), BMI (17.7±2.8, kg/m²). Dual energy X-ray absorptiometry (DXA) was chosen as a reference method, despite some minor bias, as it is considerably less expensive and difficult to administer in pediatric samples than other established "gold standard" reference body composition methods. Study characteristic variables are shown (p value: females vs males). Variables Females (25) Males (50) p value Z(Ω₅₀) 737.0±76.8 631.2±60.2 <0.0001 ZI (cm²/Ω₅₀) 26.6±7.6 31.0±5.7 0.006 FFM_DXA 23.8±6.1 25.7±3.8 0.10 ZI values were highly correlated with FFM measured by DXA. The following equations were obtain from the regression analysis: Males, FFM_DXA = 0.6375 (ZI) + 5.9913, R² = 0.897, p<0.0001. Females, FFM_DXA = 0.7597 (ZI)+ 3.5853, R² = 0.903, p<0.0001. These data supported that BIA alone can be used as a surrogate to measure FFM in pediatric sample.