title: Agreement between circulating IGF-I, IGFBP-1 and IGFBP-3 levels measured by current assays versus unavailable assays previously used in epidemiological studies.
abstract: OBJECTIVE
  Levels of insulin-like growth factor (IGF) proteins are associated with the risk of cancer and mortality. IGF assays produced by Diagnostic Systems Laboratories (DSL) were widely used in epidemiological studies, were not calibrated against recommended standards and are no longer commercially available.
  
  
  METHODS
  In a split sample study among 1471 adults participating in the Cardiovascular Health Study, we compared values obtained using DSL assays with alternative assays for serum IGF-I (Immunodiagnostic Systems, IDS), IGFBP-1 (American Laboratory Products Company, ALPCO) and IGFBP-3 (IDS).
  
  
  RESULTS
  Results were compared using kernel density estimation plots, quartile analysis with weighted kappa statistics and linear regression models to assess the concordance of data from the different assays. Participants had a mean age of 77years. Results between alternative assays were strongly correlated (IGF-I, r=0.93 for DSL versus IDS; log-IGFBP-1, r=0.90 for DSL versus ALPCO; IGFBP-3, r=0.92 for DSL versus IDS). Cross tabulations showed that participants were usually in the same quartile categories regardless of the assay used (overall agreement, 74% for IGF-I, 64% for IGFBP-1, 71% for IGFBP-3). Weighted kappa also showed substantial agreement between assays (kw, 0.78 for IGF-I, 0.69 for IGFBP-1, 0.76 for IGFBP-3). Regressions of levels obtained with DSL assays (denoted X) to alternative assays were, IGF-I: 0.52X+15.2ng/ml, log-IGFBP-1: 1.01X-1.73ng/ml IGFBP-3: 0.87X+791.1ng/ml. Serum values of IGF-I, IGFBP-1 and IGFBP-3 measured using alternative assays are moderately correlated.
  
  
  CONCLUSIONS
  Care is needed in the interpretation of data sets involving IGF analytes if assay methodologies are not uniform.
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, United States. Electronic address: chino.aneke@med.einstein.yu.edu.
authors.forename: Chino S
authors.initials: CS
authors.lastname: Aneke-Nash
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, WA, United States.
authors.forename: Clara
authors.initials: C
authors.lastname: Dominguez-Islas
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, WA, United States.
authors.forename: Petra
authors.initials: P
authors.lastname: Bůžková
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, United States.
authors.forename: Qibin
authors.initials: Q
authors.lastname: Qi
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, United States.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Xue
authors.affiliation: Department of Medicine and Oncology, McGill University, Montreal, Quebec, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Pollak
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, United States.
authors.forename: Howard D
authors.initials: HD
authors.lastname: Strickler
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY, United States.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Kaplan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000032:analysis / Q000097:blood*; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000032:analysis / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000378:metabolism; D008297:Male; D015203:Reproducibility of Results
chemical_list: D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I
keywords: Diabetes; Glycemic status; Insulin-like growth factor