Variations in the measurement of resting energy expenditure in children with cystic fibrosis

Objective: To investigate in children with cystic fibrosis (CF) and childre n without CF: (1) the test-retest reproducibility of a 20 min resting energ y expenditure (REE) measurement: and (2) the long-term reproducibility of R EE measurements in children with CF using longitudinal data. Design: Cross-sectional study and longitudinal cohort. Setting: A tertiary referral paediatric hospital. Subjects: A total of 31 (11 male, 20 female) children (aged 12.8 +/- 3.6 y) with CF and 32 (14 male, 18 female) healthy children without CF (aged 12.2 +/- 2.3 y) were enrolled in the short-term reproducibility study. Long-ter m REE measurement reproducibility was assessed in another 14 children (5 ma le, 9 female) with CF, comparing their initial REE measurement with a subse quent measurement 1 - 2 y later. Methods: All children had measurements of height, weight, skinfold thicknes s and indirect calorimetry. Results: There was no statistically significant difference in REE between r epeated measurements in children with CF (mean s.d., 6240 +/- 1280 and 6220 +/- 1315 kJ/24 h) and in the children without CF (6040 +/- 956 and 6015 +/ - 943 kJ/24 h). For the children with CF, the intraclass correlation coeffi cient was 0.99 and for children without CF the intraclass correlation coeff icient was 0.97. The measurement errors were 119 and 177 kJ respectively. A pproximately 80% of the variation in REE in the CF group and 70% in the gro up without CF was explained by fat-free mass (FFM). Analysis of the longitu dinal CF data show there was no difference in REE between a child's first m easurement (5140 +/- 1140 kJ) and their subsequent measurement (5460 +/- 11 90 kJ), after adjustment for changes in body size between the measurements. Conclusion: This study has demonstrated that a short-term 20 min REE measur ement is reproducible and therefore valid in children with CF and children without CF. These results also indicate that in children with CF, long-term REE measurements are reproducible.