Diabetes Antibody Standardization Program: first assay proficiency evaluation

The aims of the first proficiency evaluation of the Diabetes Antibody Standardization Program (DASP) were to assess general implementation of assay methods and to evaluate the new World Health Organization (WHO) reference reagent for autoantibodies to GAD and IA-2. Forty-six laboratories in 13 countries received coded sera from 50 patients with newly diagnosed type 1 diabetes and 50 blood donor control subjects, together with the WHO reference reagent and diluent serum. Results were analyzed using receiver operator characteristic (ROC) curves. Sensitivity was adjusted to 90% specificity in workshop controls. The median adjusted sensitivity for GADA (45 laboratories) was 84% (range 62-96%), for IA-2A (43 laboratories) was 58% (50-74%), and for insulin autoantibody (IAA; 23 laboratories) was 36% (13-66%). ROC curve analysis showed all GADA and IA-2A assays, and 18/23 IAA assays found significant differences between patients and control subjects. There was good concordance between laboratories in ranking of samples by GADA and IA-2A levels or if results were expressed in relation to the WHO reference reagent. Assays that achieved the highest sensitivity for IAA were also concordant in ranking samples, but overall concordance for IAA was poor. Differences in assay protocols between laboratories must be addressed so that all centers and kit manufacturers can perform to the same high standard.