Diagnostic accuracy of the anti‐glutamic acid decarboxylase antibody in type 1 diabetes mellitus: Comparison between radioimmunoassay and enzyme‐linked immunosorbent assay

AIMS/INTRODUCTION: The distributer of the anti‐glutamic acid decarboxylase antibody assay kit using radioimmunoassay (RIA) recently announced its discontinuation, and proposed an alternative kit using enzyme‐linked immunosorbent assay (ELISA). The aim of the present study was to investigate the diagnostic values of the anti‐glutamic acid decarboxylase antibody by RIA and ELISA among type 1 diabetes mellitus patients and control participants. MATERIALS AND METHODS: A total of 79 type 1 diabetes mellitus patients and 79 age‐matched controls were enrolled and assessed using RIA and ELISA. Sensitivity, specificity, positive predictive values and negative predictive values were calculated for cut‐off values (RIA = 1.5 U/mL and ELISA = 5.0 U/mL, respectively). Kappa coefficients were used to test for agreements between the RIA and ELISA methods regarding the diagnosis of type 1 diabetes mellitus. RESULTS: The sensitivity, specificity, positive predictive values, and negative predictive values for diagnosing type 1 diabetes mellitus were 57.0, 97.5, 95.7, and 69.4% by RIA, and 60.8, 100.0, 100.0 and 71.8% by ELISA, respectively. The diagnosis of type 1 diabetes mellitus using the RIA and ELISA methods showed substantial agreement with the kappa values of 0.74 for all participants, and of 0.64 for the acute type; however, there was moderate agreement with the kappa value of 0.56 for the slowly progressive type. CONCLUSIONS: The present study suggests that both anti‐glutamic acid decarboxylase antibody by RIA and ELISA was useful for diagnosing type 1 diabetes mellitus. However, in the slowly progressive type, the degree of agreement of these two kits was poorer compared with those in all participants or in the acute type.