title: Five commercially available insulin-like growth factor I (IGF-I) assays in comparison to the former Nichols Advantage IGF-I in a growth hormone treated population.
abstract: BACKGROUND
  The serum insulin-like growth factor I (IGF-I) level is accepted to diagnose the growth hormone (GH) status. Here, we evaluated the DRG IGF-I 600 ELISA, DSL IGF-I ELISA, IDS OCTEIA IGF-I, Mediagnost IGF-I-ELISA, and the Siemens Immulite 2500 IGF-I in comparison to the former Nichols Advantage IGF-I assay.
  
  
  METHODS
  Imprecision was determined by use of a serum pool and commercial control materials. Accuracy was evaluated by means of a method comparison to Nichols in 173 serum samples of GH deficient patients.
  
  
  RESULTS
  The Siemens and the IDS IGF-I assays showed the lowest imprecision with coefficients of variation up to 3.6% and 6.9%, respectively. Both correlated best to Nichols (Siemens: y=0.667X+8.8 microg/L, r=0.950; IDS: y=0.527 X+4.6 microg/L, r=0.927) with the lowest dispersion of residuals from a linear equation. The DSL assay had the highest comparability to Nichols (y=1.000 X+35.5 microg/L, r=0.864), but with a considerable scattering.
  
  
  CONCLUSIONS
  To yield IGF-I determination comparable to the former Nichols IGF-I, either the Siemens or the IDS assay should be applied, and the results should be converted by a linear method transformation. Where a conversion factor is not desired, the DSL assay should be selected.
authors.affiliation: Institute of Clinical Chemistry and Laboratory Medicine, Ernst Moritz Arndt University of Greifswald, Greifswald, Germany. alexander.krebs@uni-greifswald.de
authors.forename: Alexander
authors.initials: A
authors.lastname: Krebs
authors.forename: Henri
authors.initials: H
authors.lastname: Wallaschofski
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Spilcke-Liss
authors.forename: Thomas
authors.initials: T
authors.lastname: Kohlmann
authors.forename: Georg
authors.initials: G
authors.lastname: Brabant
authors.forename: Henry
authors.initials: H
authors.lastname: Völzke
authors.forename: Matthias
authors.initials: M
authors.lastname: Nauck
mesh_terms: D001681:Biological Assay / Q000295:instrumentation / Q000379:methods*; D001774:Blood Chemical Analysis / Q000379:methods*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000627:therapeutic use
chemical_list: D007334:Insulin-Like Growth Factor I