1. ¹Children's Nutrition Research Centre, Department of Paediatrics and Child Health, University of Queensland, Royal Children's Hospital, Herston, Qld, 4029, Australia
2. ²Department of Respiratory Medicine, Royal Children's Hospital, Herston, Qld, 4029, Australia
3. ³Department of Paediatrics and Child Health, University of Queensland, Royal Children's Hospital, Herston, Qld, 4029, Australia
4. ⁴Department of Nuclear Medicine, Royal Brisbane Hospital, Herston, Qld, 4029, Australia

Correspondence: AJ Murphy, Body Composition Laboratory, Children's Nutrition Research Centre, Department of Paediatrics and Child Health, University of Queensland, Royal Children's Hospital, Herston, Qld, 4029, Australia. E-mail: alexia.murphy@uq.edu.au

Guarantor: AJ Murphy.

Contributors: AJM was responsible for study design, performing the ADP measurements, interpreting the results and writing of the paper. HMB was responsible for study design, coordinating the study and editing the paper. JCHW supervised the DEXA measurements and participated in editing the paper. CEW contributed to original study design, supervision of clinical aspects and editing of the paper. RMG participated in study design and editing of the paper. PSWD was involved in the study design, interpretation of the results and editing of the paper.

Received 22 April 2003; Revised 28 September 2003; Accepted 7 October 2003.

Abstract

Objectives: The purpose of this paper was to evaluate the use of air displacement plethysmography (ADP) in children and adolescents with cystic fibrosis (CF). Specifically, the primary aim of this study was to compare estimates of fat-free mass (FFM) measured from ADP and dual energy X-ray absorptiometry (DEXA) in children and adolescents with CF. The secondary aim was to compare the effect of using predicted thoracic gas volume (V _TG) and measured V _TG for the calculation of FFM by ADP in this population.

Methods: Cross-sectional FFM measurements were taken using ADP and DEXA in 52 children and adolescents with CF, ranging in age from 6.3 to 16.6 y.

Results: Bland–Altman analysis showed that ADP values of FFM were on average 0.59 kg higher than DEXA values (95% limits of agreement = 3.61 to -2.43 kg); however this difference was not significant. There was no significant correlation (r=-0.26, P=0.07) between the mean FFM and difference in FFM between ADP and DEXA. Using either predicted or measured V _TG did not significantly affect FFM estimates in individuals with CF who had normal lung function (bias=-0.390.86 kg; r=-0.02, P=0.93).

Conclusions: ADP is an appropriate technique for use in children and adolescents with CF.