title: Evaluation of Lunar Prodigy dual-energy X-ray absorptiometry for assessing body composition in healthy persons and patients by comparison with the criterion 4-component model.
abstract: BACKGROUND
  Dual-energy X-ray absorptiometry (DXA) is widely used to assess body composition in research and clinical practice. Several studies have evaluated its accuracy in healthy persons; however, little attention has been directed to the same issue in patients.
  
  
  OBJECTIVE
  The objective was to compare the accuracy of the Lunar Prodigy DXA for body-composition analysis with that of the reference 4-component (4C) model in healthy subjects and in patients with 1 of 3 disease states.
  
  
  METHODS
  A total of 215 subjects aged 5.0-21.3 y (n = 122 healthy nonobese subjects, n = 55 obese patients, n = 26 cystic fibrosis patients, and n = 12 patients with glycogen storage disease). Fat mass (FM), fat-free mass (FFM), and weight were measured by DXA and the 4C model.
  
  
  RESULTS
  The accuracy of DXA-measured body-composition outcomes differed significantly between groups. Factors independently predicting bias in weight, FM, FFM, and percentage body fat in multivariate models included age, sex, size, and disease state. Biases in FFM were not mirrored by equivalent opposite biases in FM because of confounding biases in weight.
  
  
  CONCLUSIONS
  The bias of DXA varies according to the sex, size, fatness, and disease state of the subjects, which indicates that DXA is unreliable for patient case-control studies and for longitudinal studies of persons who undergo significant changes in nutritional status between measurements. A single correction factor cannot adjust for inconsistent biases.
authors: MRC Childhood Nutrition Research Centre, Institute of Child Health, London, UK. jane.williams@ich.ucl.ac.uk
authors: Jane E
authors: JE
authors: Williams
authors: Jonathan C K
authors: JC
authors: Wells
authors: Catherine M
authors: CM
authors: Wilson
authors: Dalia
authors: D
authors: Haroun
authors: Alan
authors: A
authors: Lucas
authors: Mary S
authors: MS
authors: Fewtrell