title: Pilot study for the standardization of insulin immunoassays with isotope dilution liquid chromatography/tandem mass spectrometry.
abstract: BACKGROUND
  An international working group convened by the American Diabetes Association (ADA) called for a reference measurement procedure for use in a trueness-based standardization project of insulin immunoassays. In view of this demand, we conducted a pilot study to investigate the feasibility of such a standardization project with our isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/tandem MS) procedure.
  
  
  METHODS
  We evaluated the precision, accuracy, and limit of quantification (LoQ) of the ID-LC/tandem MS procedure by use of insulin-free serum supplemented with insulin to give 3 pools with concentrations of 0.0796, 0.769, and 5.56 microg/L. We conducted a pilot method comparison study with 4 immunoassays and 80 samples from fasting and glucose-stimulated patients.
  
  
  RESULTS
  The within-run and total imprecision (CV) ranged from 3.2% to 6.3% and from 4.9% to 12.1% (listing sequence from the high to the low pool). The recovery from supplemented insulin-free sera ranged from 101.8% to 104.1%, and the LoQ was 0.07 microg/L (12 pmol/L). Weighted Deming regression and correlation analysis of the method-comparison data showed considerable between-assay variation for the immunoassays but, with the exception of one assay, excellent correlation with ID-LC/tandem MS. Recalibration of the immunoassay results considerably reduced the between-assay variation. Moreover, after recalibration, 3 of the 4 assays fulfilled the total error specification of 32% proposed by the ADA Workgroup.
  
  
  CONCLUSIONS
  Recalibration of insulin assays by regression equations established from method comparison with ID-LC/tandem MS can result in successful standardization and fulfillment of the total error criterion proposed by the ADA Workgroup.
authors.affiliation: Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium.
authors.forename: Diego
authors.initials: D
authors.lastname: Rodríguez-Cabaleiro
authors.forename: Katleen
authors.initials: K
authors.lastname: Van Uytfanghe
authors.forename: Veronique
authors.initials: V
authors.lastname: Stove
authors.forename: Tom
authors.initials: T
authors.lastname: Fiers
authors.forename: Linda M
authors.initials: LM
authors.lastname: Thienpont
mesh_terms: D002138:Calibration; D002853:Chromatography, Liquid; D005215:Fasting; D005240:Feasibility Studies; D005947:Glucose; D018149:Glucose Intolerance / Q000175:diagnosis; D006801:Humans; D007118:Immunoassay / Q000592:standards; D007201:Indicator Dilution Techniques; D007328:Insulin / Q000097:blood*; D007333:Insulin Resistance; D009765:Obesity / Q000175:diagnosis; D010865:Pilot Projects; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D007328:Insulin; D005947:Glucose