title: Reference ranges of serum IGF-1 and IGFBP-3 levels in a general adult population: results of the Study of Health in Pomerania (SHIP).
abstract: OBJECTIVE
  Insulin-like growth factor I (IGF-1), which is mostly carried by IGF binding protein 3 (IGFBP-3), mediates endocrine actions of growth hormone and represents an important prognostic factor for systemic diseases. The main objectives of the present study were (1) to calculate age- and sex-specific reference values for serum IGF-1 and IGFBP-3 levels using the Gaussian mean+/-1.96 *standard deviation method and the quantile regression method and (2) to perform a comparison of the results from both statistical methods.
  
  
  METHODS
  Cross-sectional study (Study of Health in Pomerania). The study population included 2499 men and women aged 20-79 years.
  
  
  METHODS
  Serum IGF-1 and IGFBP-3 levels were determined by chemiluminescence immunoassays. Linear and quantile regressions were performed to calculate age- and sex-related reference ranges.
  
  
  RESULTS
  Both statistical methods generated different results: The reference ranges based on linear regression identified 43 (1.7%) subjects with serum IGF-1 levels and 99 (4.0%) subjects with serum IGFBP-3 levels outside the reference range. Using quantile regression, 117 (4.7%) or 118 subjects (4.7%) with serum IGF-1 or IGFBP-3 levels outside the range were detected, respectively.
  
  
  CONCLUSIONS
  The present study established age- and sex-specific reference ranges for serum IGF-1 and IGFBP-3 levels. Quantile regression should be preferred to calculate reference ranges because a better concordance to original data is possible due to no distribution assumption are required and the robustness against outliers is given.
authors.affiliation: Institute for Community Medicine, Ernst Moritz Arndt University, Walther-Rathenau-Strasse 48, D-17487 Greifswald, Germany. nele.friedrich@uni-greifswald.de
authors.forename: Nele
authors.initials: N
authors.lastname: Friedrich
authors.forename: Dietrich
authors.initials: D
authors.lastname: Alte
authors.forename: Henry
authors.initials: H
authors.lastname: Völzke
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Spilcke-Liss
authors.forename: Jan
authors.initials: J
authors.lastname: Lüdemann
authors.forename: Markus M
authors.initials: MM
authors.lastname: Lerch
authors.forename: Thomas
authors.initials: T
authors.lastname: Kohlmann
authors.forename: Matthias
authors.initials: M
authors.lastname: Nauck
authors.forename: Henri
authors.initials: H
authors.lastname: Wallaschofski
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000097:blood; D005260:Female; D005858:Germany; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012044:Regression Analysis; D012727:Sex Characteristics
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I