ABILITY OF BIOLECTRIC IMPEDANCE TO PREDICT FAT-FREE MASS IN PREPUBERTAL CHILDREN

Measurements of body composition are being made increasingly widely in pediatrics. Tetrapolar whole body impedance (BI) is particularly suit able as a method of estimating body composition in children and is the refore the subject of great interest at present. However, the ability of BI to accurately estimate fat-free mass (FFM) in children is unclea r, and users of BI are faced with a growing choice of prediction equat ions for estimation of FFM. Studies in adults have suggested that choi ce of prediction equation can have a profound effect on the estimate o btained, The aim of the present study was to measure the ability of fo ur published pediatric BI equations to predict FFM in 98 Caucasian pre pubertal children (mean age 9.0 y). For three of the published equatio ns, limits of agreement between predicted and reference FFM were wide and distinct biases were apparent. With mean FFM of 25 kg, the equatio n of L. Cordain et al. overestimated reference FFM (95% CI +2.1 to +3. 1 kg), whereas those of P. Deurenberg ct al. (95% CI -1.9 to -2.9 kg) and F. Schaefer ct al. (95% CI -1.4 to -2.5 kg) systematically underes timated reference FFM. The equation of Houtkooper et al. (95% CI -0.2 to +0.8 kg) predicted FFM with negligible bias and had narrower limits of agreement relative to the reference method than the other three eq uations tested. We conclude that the ability of BI to predict body com position in children depends on the equation chosen and that the gener al applicability of BI equations cannot be safely assumed. Cross-valid ation of BI equations is recommended before they are used routinely fo r estimation of body composition in children.