title: Validation of functional insulin-like growth factor binding protein-3 measurement by a ligand immunoassay.
abstract: BACKGROUND
  Proteolysis of Insulin-like Growth Factor Binding Protein (IGFBP)--3 is a well known mechanism regulating IGF-I bioavailability and IGF-independent actions of IGFBP-3 fragments. Measurement of functional IGFBP-3 can be of use in diagnostics of growth failure or renal impairment. We herein characterize the properties of a commercially available immunoassay for the measurement of functional (IGF-I binding) IGFBP-3.
  
  
  METHODS
  Fragmentation of IGFBP-3 is analyzed by gel filtration, SDS-PAGE, and western ligand and immunoblotting and compared with subsequent measurement of total and functional IGFBP-3 by ELISA/IFA. Furthermore, assay characteristics such as reproducibility, linearity, and sensitivity are surveyed.
  
  
  RESULTS
  Functional IGFBP-3 was reproducibly measured (6.8/5.6% Inter-/Intra assay variance). A broad range of linearity (1:50-1:300) and a high sensitivity (0.18 microg/L) allowed reliable measurement of IGF-binding IGFBP-3. Analysis of IGFBP-3 fragments reveals that the assay described only detects intact IGFBP-3. Analysis of 189 serum samples from healthy blood donors showed that on average 84% and 69% of total IGFBP-3 was functional in men and women, respectively (p < 0.01).
  
  
  CONCLUSIONS
  Functional IGFBP-3 can be measured reliably by the assay system used. Thus, this assay system is suited for the investigation of the diagnostic value of functional IGFBP-3 in human body fluids.
authors.affiliation: Mediagnost GmbH, Reutlingen, Germany. langkamp@mediagnost.de
authors.forename: M
authors.initials: M
authors.lastname: Langkamp
authors.forename: K
authors.initials: K
authors.lastname: Weber
authors.forename: M
authors.initials: M
authors.lastname: Kirschner
authors.forename: L
authors.initials: L
authors.lastname: Pridzun
authors.forename: M B
authors.initials: MB
authors.lastname: Ranke
mesh_terms: D000328:Adult; D015153:Blotting, Western; D002138:Calibration; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: C515497:IGFBP3 protein, human; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins