Total body water in children with cystic fibrosis using bioelectrical impedance

Background The aim of this study was to assess the ability of commercially available single frequency bioelectrical impedance analysis (BIA) to predict total body water and hence body composition in a cohort of children with cystic fibrosis (CF). Methods In 56 (31 girls, 25 boys) children aged 4 to 18 years, total body water was predicted using BIA and measured using a deuterium oxide dilution technique. Each child provided a urine sample before consuming 0.5 g/kg body weight 10% deuterium oxide. A further urine sample was collected between 4 and 6 h later. Results There was a mean bias between predicted and measured total body water of 1.1 L. The bias was consistent across the range of total body water measured in this study.The relationship between height2/impedance and measured total body water was TBW=0.35+0.74*height2/impedance. This equation is similar to other equations found in healthy children. Conclusion We have shown that a commercially available bioelectrical device underestimates measured total body water. We have generated a prediction equation for the population studied, which we believe might enhance the accuracy of the method in children with cystic fibrosis.