Developing a model for estimating lean body weight in children

Background: Body composition changes in relation to age and maturation. Mathematical models for estimating lean body weight (LBW) have been developed in adults. There are currently no models available to predict LBW in children as a function of age or maturation. Aim: To develop a semi-mechanistic model to estimate LBW in paediatric patients.

Methods: (1)Using NONMEM® v6.0, a general model for maturation was developed for LBW. A large data set of children (496 females and 515 males) containing demographic data and body composition measurements was used to estimate model parameters. Missing data were imputed. (2)From the data set, an empirical model was developed using STATA® v11 to estimate LBW. (3)The predictive ability of the adult model and the general maturation model were evaluated using the mean squared error (MSE) in respect to the empirical model.

Results: (1)A semi-mechanistic sigmoid Emax maturation model was developed which links LBW to age: LBW = [baselineLBW + AGE^gamma/(AGE^gamma + AGE50^gamma)] * LBWadults , with AGE50 and gamma dependent on sex (2)An empirical model with 9 terms (including interactions) was developed using mixed-effect linear regression. (3)The increment in MSE using the adult model in relation to the empirical model was 133%, the increment in MSE assuming the form of the general model in relation to the empirical model was calculated to be 42%.

Conclusion: A general model for maturation for LBW in children was developed. This was compared to an empirical model for a large children dataset and was found to perform well with an MSE loss of 42%.