title: Evaluation of DXA against the four-component model of body composition in obese children and adolescents aged 5-21 years.
abstract: BACKGROUND
  Body composition is increasingly measured in pediatric obese patients. Although dual-energy X-ray absorptiometry (DXA) is widely available, and is precise, its accuracy for body composition assessment in obese children remains untested.
  
  
  OBJECTIVE
  We aimed to evaluate DXA against the four-component (4C) model in obese children and adolescents in both cross-sectional and longitudinal contexts.
  
  
  METHODS
  Body composition was measured by DXA (Lunar Prodigy) and the 4C model in 174 obese individuals aged 5-21 years, of whom 66 had a second measurement within 1.4 years. The Bland-Altman method was used to assess agreement between techniques for baseline body composition and change therein.
  
  
  RESULTS
  A significant minority of individuals (n=21) could not be scanned successfully due to their large size. At baseline, in 153 individuals with complete data, DXA significantly overestimated fat mass (FM; Delta=0.9, s.d. 2.1 kg, P<0.0001) and underestimated lean mass (LM; Delta=-1.0, s.d. 2.1 kg, P<0.0001). Multiple regression analysis showed that gender, puberty status, LM and FM were associated with the magnitude of the bias. In the longitudinal study of 51 individuals, the mean bias in change in fat or LM did not differ significantly from zero (FM: Delta=-0.02, P=0.9; LM: Delta=0.04, P=0.8), however limits of agreement were wide (FM: +/-3.2 kg; LM: +/-3.0 kg). The proportion of variance in the reference values explained by DXA was 76% for change in FM and 43% for change in LM.
  
  
  CONCLUSIONS
  There are limitations to the accuracy of DXA using Lunar Prodigy for assessing body composition or changes therein in obese children. The causes of differential bias include variability in the magnitude of tissue masses, and stage of pubertal development. Further work is required to evaluate this scenario for other DXA models and manufacturers.
authors.affiliation: Childhood Nutrition Research Centre, UCL Institute of Child Health, London, UK. J.Wells@ich.ucl.ac.uk
authors.forename: J C K
authors.initials: JC
authors.lastname: Wells
authors.forename: D
authors.initials: D
authors.lastname: Haroun
authors.forename: J E
authors.initials: JE
authors.lastname: Williams
authors.forename: C
authors.initials: C
authors.lastname: Wilson
authors.forename: T
authors.initials: T
authors.lastname: Darch
authors.forename: R M
authors.initials: RM
authors.lastname: Viner
authors.forename: S
authors.initials: S
authors.lastname: Eaton
authors.forename: M S
authors.initials: MS
authors.lastname: Fewtrell
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000293:Adolescent; D000704:Analysis of Variance; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008954:Models, Biological; D009765:Obesity / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011877:Radionuclide Imaging; D012016:Reference Values; D055815:Young Adult