A Considerable Mismatch of Measurements between Radioimmunoassay and Enzyme-Linked Immunosorbent Assay Tests for Anti-Glutamic Acid Decarboxylase Antibody

Most cases of type 1 diabetes mellitus are considered to be caused by pancreatic β-cell destruction through islet cell autoimmunity. Anti-glutamic acid decarboxylase antibody (GADA) is an important islet cell-associated autoantibody in the diagnosis of autoimmune type 1 diabetes mellitus. In Japan, the GADA assay kit was changed from radioimmunoassay (RIA) to enzyme-linked immunosorbent assay (ELISA) in 2015. Thereafter, a mismatch of measurements between the two tests became apparent in clinical situations. The aim of this study was to clarify the extent of the mismatch between the two tests on a larger scale. In this cross-sectional non-local/non-hospital-based study, we collected anonymized data on GADA levels of 598 randomly selected participants in whom GADA levels were simultaneously measured by GADA-RIA and GADA-ELISA tests. We found that 34% (= 162/477) of the GADA-RIA-positive participants showed negative results in the GADA-ELISA test; the mismatch was predominantly observed in participants with relatively low GADA-RIA levels. Concretely, when considering lower GADA-RIA levels alone (1.5-32 U/mL), GADA-ELISA-negative participants accounted for 44.8% (= 162/362) of the GADA-RIA-positive participants. These findings suggest that a single application of the GADA-ELISA test may affect the precise diagnosis of type 1 diabetes mellitus, and cause physicians’ confusion on the diagnosis. Therefore, the cause for the mismatch should be promptly identified. Disclosure Y. Oikawa: None. T. Kondo: None. A. Shimada: Advisory Panel; Self; Terumo Medical Corporation. Speaker's Bureau; Self; Abbott, Eli Lilly and Company, Novo Nordisk A/S, Sanofi-Aventis. Y. Seino: Research Support; Self; Arkray, Inc., Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company, Merck & Co., Inc., Novo Nordisk Inc., Ono Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takeda Pharmaceutical Company Limited, Terumo Medical Corporation. M. Kitaoka: Research Support; Self; AstraZeneca, Ono Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd.