title: Cross-validation of bioelectrical impedance analysis for the assessment of body composition in a representative sample of 6- to 13-year-old children.
abstract: OBJECTIVE
  (1) To cross-validate tetra- (4-BIA) and octopolar (8-BIA) bioelectrical impedance analysis vs dual-energy X-ray absorptiometry (DXA) for the assessment of total and appendicular body composition and (2) to evaluate the accuracy of external 4-BIA algorithms for the prediction of total body composition, in a representative sample of Swiss children.
  
  
  METHODS
  A representative sample of 333 Swiss children aged 6-13 years from the Kinder-Sportstudie (KISS) (ISRCTN15360785). Whole-body fat-free mass (FFM) and appendicular lean tissue mass were measured with DXA. Body resistance (R) was measured at 50 kHz with 4-BIA and segmental body resistance at 5, 50, 250 and 500 kHz with 8-BIA. The resistance index (RI) was calculated as height(2)/R. Selection of predictors (gender, age, weight, RI4 and RI8) for BIA algorithms was performed using bootstrapped stepwise linear regression on 1000 samples. We calculated 95% confidence intervals (CI) of regression coefficients and measures of model fit using bootstrap analysis. Limits of agreement were used as measures of interchangeability of BIA with DXA.
  
  
  RESULTS
  8-BIA was more accurate than 4-BIA for the assessment of FFM (root mean square error (RMSE)=0.90 (95% CI 0.82-0.98) vs 1.12 kg (1.01-1.24); limits of agreement 1.80 to -1.80 kg vs 2.24 to -2.24 kg). 8-BIA also gave accurate estimates of appendicular body composition, with RMSE < or = 0.10 kg for arms and < or = 0.24 kg for legs. All external 4-BIA algorithms performed poorly with substantial negative proportional bias (r> or = 0.48, P<0.001).
  
  
  CONCLUSIONS
  In a representative sample of young Swiss children (1) 8-BIA was superior to 4-BIA for the prediction of FFM, (2) external 4-BIA algorithms gave biased predictions of FFM and (3) 8-BIA was an accurate predictor of segmental body composition.
authors.affiliation: Institute of Exercise and Health Sciences, University of Basel, Basel, Switzerland. susi.kriemler@unibas.ch
authors.forename: S
authors.initials: S
authors.lastname: Kriemler
authors.forename: J
authors.initials: J
authors.lastname: Puder
authors.forename: L
authors.initials: L
authors.lastname: Zahner
authors.forename: R
authors.initials: R
authors.lastname: Roth
authors.forename: C
authors.initials: C
authors.lastname: Braun-Fahrländer
authors.forename: G
authors.initials: G
authors.lastname: Bedogni
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue; D000293:Adolescent; D000465:Algorithms; D000886:Anthropometry; D001823:Body Composition; D049628:Body Size; D002648:Child; D017097:Electric Impedance; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015203:Reproducibility of Results; D013557:Switzerland