title: Expected body weight in adolescents: comparison between weight-for-stature and BMI methods.
abstract: OBJECTIVE
  To test the hypothesis that the weight-for-stature (WFS) and BMI methods are not equivalent in determining expected body weight (EBW) in adolescents with eating disorders and to determine the sensitivity, specificity, and positive predictive value of each method to detect those <75% EBW. We hypothesized that differences in EBW would be greatest at the extremes of height.
  
  
  METHODS
  EBW was determined for 12 047 individual adolescents aged 12 to 19 years by the WFS and BMI methods by utilizing the same National Center for Health Statistics data sets. Absolute difference between the 2 methods for each individual was calculated and plotted against height by using a generalized additive model. The number of individuals whose weights were <75% EBW was determined by each method.
  
  
  RESULTS
  For girls, EBW was 3.52 ± 3.13% higher when using the WFS method compared with the BMI method. For boys, EBW(WFS) was 3.45 ± 2.72% higher than EBW(BMI). Among adolescent girls, 65% had EBW(WFS) higher than EBW(BMI). By using the EBW(WFS) method as the gold standard, specificity of the EBW(BMI) method to detect those <75% EBW was 0.999, but sensitivity was only 0.329. Absolute differences in EBW were most pronounced at the extremes of height.
  
  
  CONCLUSIONS
  The WFS and BMI methods are not equivalent in determining EBW in adolescents and are not interchangeable. EBW(WFS) was ~3.5% higher than EBW(BMI). In adolescents with eating disorders, use of the BMI method will underestimate the degree of malnutrition compared with the WFS method. Which method better predicts meaningful clinical outcomes remains to be determined.
authors.affiliation: Department of Pediatrics, Division of Adolescent Medicine, Stanford University School of Medicine, Stanford, CA 94304, USA. ngolden@stanford.edu
authors.forename: Neville H
authors.initials: NH
authors.lastname: Golden
authors.forename: Wei
authors.initials: W
authors.lastname: Yang
authors.forename: Marc S
authors.initials: MS
authors.lastname: Jacobson
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Robinson
authors.forename: Gary M
authors.initials: GM
authors.lastname: Shaw
mesh_terms: D000293:Adolescent; D000856:Anorexia Nervosa / Q000175:diagnosis*; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D009749:Nutrition Surveys; D011502:Protein-Energy Malnutrition / Q000175:diagnosis*; D012016:Reference Values; D012680:Sensitivity and Specificity; D014481:United States