title: Evaluation of two nonisotopic immunoassays for determination of glutamic acid decarboxylase and tyrosine phosphatase autoantibodies in serum.
abstract: BACKGROUND
  Autoantibodies for the 65-kDa form of glutamic acid decarboxylase (GAD65) and protein tyrosine phosphatase-like protein (IA-2) are measured for risk prediction and diagnosis of autoimmune diabetes mellitus. There is a lack of adequate nonisotopic alternatives to the most widely used method for both autoantibodies, which is a radiobinding assay (RBA).
  
  
  METHODS
  We compared two commercially available immunoassays, an ELISA and a time-resolved immunofluorometric assay (TR-IFMA), with RBA.
  
  
  RESULTS
  We found excellent agreement between the RBA and ELISA for measurement of GAD65 autoantibodies (GADAs); they showed comparable analytical precision in the cutoff range and achieved similar diagnostic specificity. The ELISA identified more GADA-positive individuals among patients with new-onset type 1 diabetes than did the RBA [89% (95% confidence interval, 78-95%), vs 71% (58-82%); P <0.03]. For IA-2 autoantibodies (IA-2As), only the TR-IFMA achieved analytical performance and diagnostic accuracy comparable to that of the RBA. These results with the GADA ELISA and IA-2A TR-IFMA were consistent with those obtained blindly in the Diabetes Antibody Standardization Program 2003. The performance of the GADA TR-IFMA and IA-2A ELISA was unsatisfactory, and these tests were not subjected to clinical evaluation.
  
  
  CONCLUSIONS
  The GADA ELISA and IA-2A TR-IFMA behave comparably with RBA and are thus suitable for use in the clinical laboratory.
authors.affiliation: Institut de Recerca, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Palomer
authors.forename: Dídac
authors.initials: D
authors.lastname: Mauricio
authors.forename: José
authors.initials: J
authors.lastname: Rodríguez-Espinosa
authors.forename: Edgar
authors.initials: E
authors.lastname: Zapico
authors.forename: Carme
authors.initials: C
authors.lastname: Mayoral
authors.forename: Francesc
authors.initials: F
authors.lastname: González-Sastre
authors.forename: Alberto
authors.initials: A
authors.lastname: de Leiva
authors.forename: Francisco
authors.initials: F
authors.lastname: Blanco-Vaca
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood*; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis*; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D015200:Fluoroimmunoassay; D005968:Glutamate Decarboxylase / Q000276:immunology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases / Q000276:immunology*; D011869:Radioligand Assay; D012680:Sensitivity and Specificity; D044967:Serum
chemical_list: D001323:Autoantibodies; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; D005968:Glutamate Decarboxylase