Increased diagnosis of autoimmune childhood‐onset Japanese type 1 diabetes using a new GADAb ELISA kit, compared with a previously used GADAb RIA kit

AIMS/INTRODUCTION: We compared the results of testing for glutamic acid decarboxylase antibodies (GADAb) using a radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA) in subjects with childhood-onset type 1 diabetes mellitus (T1D). MATERIALS AND METHODS: Serum specimens were collected from 1024 Japanese cases (426 boys and 598 girls) in 2013. The median age at diagnosis was 7 years (0-18 years). The blood specimens were obtained at a median age of 13 years (2-22 years). RESULTS: Among the 628 subjects whose serum specimens were collected within 5 years after diagnosis, the rate of GADAb positivity was 47.9% using RIA and 69.4% using ELISA. The subjects were divided into four groups according to their RIA and ELISA results for GADAb as follows: Gr I (RIA+/ELISA+), Gr II (RIA+/ELISA-), Gr III (RIA-/ELISA+), and Gr IV (RIA-/ELISA-). The clinical and genetic characteristics of Gr I and Gr III were quite similar in terms of age at diagnosis, male/female ratio, relatively high positive rates for both IA-2Ab and ZnT8Ab, and HLA genotype. Gr II contained only 5 patients and was characterized by a younger age at diagnosis, low positive rates for both IA-2Ab and ZnT8Ab, and a unique HLA genotype. If the positive rates of either IA-2Ab or ZnT8Ab or both were added to the GADAb results using RIA, the percentage of autoimmune T1D increased from 47.9% to 78.5%. CONCLUSION: The diagnosis of autoimmune childhood-onset Japanese T1D increased when GADAb results were obtained using a new ELISA method, compared with a previously utilized RIA method.