32 FAT-FREE MASS (FFM) ESTIMATIONS IN INFANTS BY TOTAL BODY ELECTRICAL CONDUCTIVITY (TOBEC) AND 18-OXYGEN DILUTION

Abstract

Infant FFM can be safely and rapidly measured with good reproducibility by TOBEC. However, calibration of instruments until now has been based on carcass analysis data from minipigs. No data have been published for human infants comparing FFM estimated by TOBEC (using the minipigs calibration) with FFM calculated from TBW measurements by 18-oxygen dilution. We performed this comparison by measuring FFM by both methods in 131 healthy full-term infants aged between 1 and 12 months (♂/♀ =0.98). After a predose baseline urine sample a preweighted oral dose of 18-O enriched water was administered and a post-dose sample on days 1 and 9 was collected. TBW was calculated by extrapolation to time zero.Regression analysis of FFM by TOBEC (X) against FFM by 18-O (Y) showed a straight linear relation: Y= −0.122 (±0.078) + 0.985(±0.016) X, r=0.98, SEE=0.214 kg. No bias in the distribution of the residuals was seen.Conclusions: 1] FFM values in healthy infants measured by TOBEC and 18-oxygen are highly and strictly linearly correlated. 2] Estimation of FFM in healthy infants by TOBEC results in slightly higher FFM values than by 18-O dilution. This systematic difference is constant during the first year of life. 3] Both methods can be used for accurate estimations of fat-free mass and body fat in infants between 1 and 12 months of age.