Evaluation of two nonisotopic immunoassays for determination of glutamic acid decarboxylase and tyrosine phosphatase autoantibodies in serum.
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.
Palomer
Xavier
X
Institut de Recerca, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain.
Mauricio
Dídac
D
Rodríguez-Espinosa
José
J
Zapico
Edgar
E
Mayoral
Carme
C
González-Sastre
Francesc
F
de Leiva
Alberto
A
Blanco-Vaca
Francisco
F
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
D001323:Autoantibodies; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; D005968:Glutamate Decarboxylase