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Objective: To investigate in children with cystic fibrosis (CF) and children without CF: (1) the test-retest reproducibility of a 20 min resting energy expenditure (REE) measurement; and (2) the long-term reproducibility of REE 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-term REE measurement reproducibility was assessed in another 14 children (5 male, 9 female) with CF, comparing their initial REE measurement with a subsequent measurement 1-2 y later., Methods: All children had measurements of height, weight, skinfold thickness and indirect calorimetry., Results: There was no statistically significant difference in REE between repeated 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 coefficient was 0.99 and for children without CF the intraclass correlation coefficient was 0.97. The measurement errors were 119 and 177 kJ, respectively. Approximately 80% of the variation in REE in the CF group and 70% in the group without CF was explained by fat-free mass (FFM). Analysis of the longitudinal CF data show there was no difference in REE between a child's first measurement (5140+/-1140 kJ) and their subsequent measurement (5460+/-1190 kJ), after adjustment for changes in body size between the measurements., Conclusion: This study has demonstrated that a short-term 20 min REE measurement 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.

Objective: To assess body protein and protein deposition in prepubertal children with phenylketonuria (PKU)., Design: Cross-sectional study with nested longitudinal cohort., Setting: A tertiary referral paediatric hospital., Subjects: 37 PKU patients (3.9-11.0 years) and 27 unselected healthy controls (4.0-11.5 years) of whom 29 PKU patients and 17 controls were followed longitudinally., Interventions: All had measurements of height, weight, body fat and total body nitrogen (TBN) by neutron capture analysis; PKU patients and their unaffected siblings (n = 16) also had measurements of four day weighed food record and plasma amino acids by HPLC., Results: The children with PKU compared with the controls were significantly shorter (height SD score -0.42 +/- 0.89 vs 0.17 +/- 0.94, respectively, P < 0.02) and had a lower TBN (575 +/- 200 vs 710 +/- 215g, respectively, P < 0.02). TBN in the controls was significantly correlated with lean body mass (LBM), weight, height and age (r = 0.97, 0.95, 0.95, 0.88, respectively, P < 0.001). The children with PKU had significantly lower TBN when predicted from LBM, weight and age (93%, 92%, 92% of predicted, respectively), but normal TBN predicted from height (102% of expected). The annual accretion of nitrogen was similar for the PKU and controls (86 +/- 45 and 77 +/- 58 g/y, respectively). There was no difference between the two groups in protein intake or plasma amino acids except for phenylalanine., Conclusion: The children with PKU had a deficit in height and body protein despite a normal to higher accretion of protein. If the deficit occurs early in life, amino acid supplementation and other nutritional practices used at this time need to be reviewed.

Objective: To directly assess the body protein content of children with chronic renal failure (CRF) and short stature., Setting: A tertiary referral paediatric hospital., Subjects: There were: (i) 17 patients (10 male, nine pre-pubertal; mean age 12.90 +/- 3.20 years) with CRF and height standard deviation (SD) score < -2.00, and (ii) 43 normal children (18 male, 27 pre-pubertal; mean age 10.34 +/- 3.34 years)., Interventions: CRF patients had the following measurements: anthropometry, total body nitrogen (TBN) by neutron capture analysis, 4 day weighed food record and serum albumin levels. Control subjects had TBN and anthropometric measurements only., Results: Although older than the controls, the CRF patients had significantly lower TBN values (645 +/- 265 vs 930 +/- 365 g, P < 0.01). Mean values for TBN and TBN/height (percentages of expected) in the CRF patients were significantly reduced to 54% and 63% respectively, when predicted from age. However, their TBN predicted from height was 100% of expected. %TBN (predicted from age) correlated significantly with height SD score (r = 0.79), weight SD score (r = 0.87), upper arm muscle area percentile (r = 0.62) and serum albumin (r = 0.62). Mean oral energy and protein intakes were 65% and 172% of recommended dietary intake respectively., Conclusions: Children with CRF and short stature are significantly protein-depleted for age although not for height. Chronic energy deficiency may contribute to impaired protein deposition which, in turn, may be important in the pathogenesis of growth failure in CRF.

The total body protein status of 18 patients undergoing regular haemodialysis was assessed by measuring total body nitrogen (TBN) using in vivo neutron activation analysis (NAA). Eighteen healthy controls, who were selected according to their height, age and sex match with the patients were also measured. The male and female patients were both found to have lower mean values for total body protein (P less than 0.01, P less than 0.025 respectively) although they had similar weights compared with their matched controls. Seven patients were measured on further occasions and only two patients showed a change in their body protein. One female showed an increase of 11 per cent in body protein (with an increase of 25 per cent in body weight) after intensive nutritional repletion therapy. In vivo NAA provides a direct means of measuring body protein and is a reliable method to monitor changes with treatment regimes.