Pancreas Islet Cell-Specific Antibody Detection by ELISA

Islet cell-specific autoantibodies are useful to classify diabetes. The aim of this study was to evaluate the performance of commercially available ELISAs to detect autoantibodies to glutamic acid decarboxylase 65-kDa isoform (GADA), tyrosine phosphatase-related islet antigen 2 (IA-2A), zinc transporter protein 8 (ZnT8A), and insulin (IAA). The performance of ELISA was compared to the performance of RIA.

We retrospectively identified 76 newly diagnosed type 1 diabetes mellitus patients (median age 27 years, female/male: 0.65) and 131 disease controls (median age 45 years, female/male: 0.60). The ELISAs were from Medipan. RIAs were in-house methods from the Belgian Diabetes Registry or from Medipan or DIASource.

Sensitivity and specificity of ELISA were, respectively, 97% and 97% for GADA, 61% and 99% for IA-2A, 1% and 96% for IAA, and 70% and 98% for ZnT8A. The likelihood ratio for type 1 diabetes increased with increasing antibody levels for GADA, IA-2A, and ZnT8A measured by ELISA. The positive predictive value of double positivity for either GADA, IA-2A, or ZnT8A was 100%.

The ELISAs to detect GADA, IA-2A, and ZnT8A have good performance characteristics. Combining autoantibody assays and taking into account antibody levels improves the interpretation of autoantibody testing.