Actual condition survey regarding mismatch of measurements between radioimmunoassay and enzyme‐linked immunosorbent assay tests for anti‐glutamic acid decarboxylase antibody in real‐world clinical practice

Anti‐glutamic acid decarboxylase antibody (GADA) is an important islet cell‐associated autoantibody for the diagnosis of autoimmune type 1 diabetes mellitus. In Japan, the GADA assay kit was recently changed from radioimmunoassay (RIA) to enzyme‐linked immunosorbent assay (ELISA). Thereafter, a mismatched measurement between the two tests became apparent in clinical situations. The present study aimed to clarify the actual extent of mismatch between the two measurements on a larger‐scale real‐world clinical practice. In this cross‐sectional non‐local/non‐hospital‐based study, we collected anonymized data on GADA levels of 598 participants, who were simultaneously measured with GADA‐RIA and GADA enzyme‐linked immunosorbent assay tests. We found that 34% of the GADA‐RIA‐positive participants showed negative results in the GADA enzyme‐linked immunosorbent assay test; the mismatch was predominantly observed in participants with relatively low GADA‐RIA levels (<32 U/mL). This considerable mismatch might lead to physicians’ confusion in diagnosing type 1 diabetes mellitus.