New equations for estimating body cell mass from bioimpedance parallel models in healthy older Germans

The objectives of this study were to assess for elderly Germans the validit y of existing equations for predicting body cell mass (BCM) and to develop from single- and multifrequency bioimpedance (SFBIA, MFBIA) models new pred iction equations. In a data-splitting approach, validation and cross-valida tion were performed in 160 healthy elderly (60- to 90-yr) subjects. BCM was determined using a tetrapolar bioimpedance analyzer (800 muA; 4 fixed freq uencies: 1, 5, 50, and 100 kHz; electrodes placed to hand, wrist, ankle, an d foot) and whole body K-40 counting as a reference method. New prediction equations were derived by multiple stepwise regression analysis. The Bland- Altman procedure was used for methods comparison. Relative to whole body co unting, the manufacturer's equation overestimated BCM by 9% in men (P < 0.0 001, paired t-test) and 4% in women (P = 0.002). Compared with the manufact urer's equation, the newly derived equations (r = 0.92, RMSE = 6-9%) improv ed accuracy (pure error = 13 vs. 7-8%) and reduced bias and limits of agree ment. SFBIA and MFBIA equations did not differ in precision or accuracy. We conclude that the newly derived equations improved BCM estimates in the el derly compared with existing equations. There was no advantage of MFBIA ove r SFBIA equations.