title: Evaluation of four methods used to measure plasma insulin-like growth factor 1 concentrations in healthy cats and cats with diabetes mellitus or other diseases.
abstract: OBJECTIVE
  To evaluate 4 methods used to measure plasma insulin-like growth factor (IGF) 1 concentrations in healthy cats and cats with diabetes mellitus or other diseases.
  
  
  METHODS
  39 healthy cats, 7 cats with diabetes mellitus, and 33 cats with other diseases.
  
  
  METHODS
  4 assays preceded by different sample preparation methods were evaluated, including acid chromatography followed by radioimmunoassay (AC-RIA), acid-ethanol extraction followed by immunoradiometry assay (AEE-IRMA), acidification followed by immunochemiluminescence assay (A-ICMA), and IGF-2 excess followed by RIA (IE-RIA). Validation of the methods included determination of precision, accuracy, and recovery. The concentration of IGF-1 was measured with all methods, and results were compared among cat groups.
  
  
  RESULTS
  The intra-assay coefficient of variation was < 10% for AC-RIA, A-ICMA, and AEE-IRMA and 14% to 22% for IE-RIA. The linearity of dilution was close to 1 for each method. Recovery rates ranged from 69% to 119%. Five healthy cats had IGF-1 concentrations > 1,000 ng/mL with the AEE-IRMA, but < 1,000 ng/mL with the other methods. Compared with healthy cats, hyperthyroid cats had significantly higher concentrations of IGF-1 with the A-ICMA method, but lower concentrations with the IE-RIA method. Cats with lymphoma had lower IGF-1 concentrations than did healthy cats regardless of the method used.
  
  
  CONCLUSIONS
  Differences in the methodologies of assays for IGF-1 may explain, at least in part, the conflicting results previously reported in diabetic cats. Disorders such as hyperthyroidism and lymphoma affected IGF-1 concentrations, making interpretation of results more difficult if these conditions are present in cats with diabetes mellitus.
authors.affiliation: Clinic for Small Animal Internal Medicine, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland.
authors.forename: Flurin
authors.initials: F
authors.lastname: Tschuor
authors.forename: Eric
authors.initials: E
authors.lastname: Zini
authors.forename: Stefan
authors.initials: S
authors.lastname: Schellenberg
authors.forename: Monique
authors.initials: M
authors.lastname: Wenger
authors.forename: Felicitas S
authors.initials: FS
authors.lastname: Boretti
authors.forename: Claudia E
authors.initials: CE
authors.lastname: Reusch
mesh_terms: D000818:Animals; D002371:Cat Diseases / Q000097:blood*; D002415:Cats / Q000097:blood*; D003920:Diabetes Mellitus / Q000097:blood / Q000662:veterinary*; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008163:Luminescent Measurements / Q000379:methods* / Q000662:veterinary; D008297:Male; D011863:Radioimmunoassay / Q000379:methods* / Q000662:veterinary
chemical_list: D007334:Insulin-Like Growth Factor I