Measurement of Pancreatic Islet Cell Autoantibodies by ELISA and RIA in Patients with Diabetes Mellitus

Song, Jae Woo; Kim, Kyong Rae; Nam, Su Youn; Kim, Duk Hee; Lee, Anna; Kim, Moon Hee; Song, Kyung Soon; Kim, Hyon Suk

Abstract

BACKGROUND
The isoenzyme of glutamate decarboxylase (GAD), islet associated antigen (IA2, IAA) and insulin are known to be the major target antigens of pancreatic islet cell autoantibody as a predictor of type 1 diabetes mellitus (DM). Generally radioimmunoassay (RIA) methods are used for these autoantibodies but inconvenience of dealing with radioisotope have made enzyme-linked immunosorbent assay (ELISA) developed for clinical utilization. But, lack of evaluation or comparison studies of these two methods for autoantibodies make laboratories hesitate to adopt.
METHODS
We measured the glutamate decarboxylase autoantibody (GADA), insulin autoantibody (IAA) and pancreatic islet cell autoantibodies (ICA) by a commercial ELISA method in 34 patients with type 1 DM, and 31 patients with type 2 DM, and 32 healthy control group. Conventional RIA was performed concurrently and compared for GADA and IAA. ICA was measured by conventional indirect immunofluorescent assay (IFA). The obtained results were compared and also C-peptide level was measured as a marker for residual function of islet cell of pancreas.
RESULTS
Each autoantibody measured by ELISA in type 1 DM showed positive rate of 11.8% and for ICA, 26.5% for GADA, and 35.3% for IAA. The positive rate of the same group of type 1 DM when using RIA were 76.5% for GADA far exceeding that of ELISA method, and 29.4% for IAA. The percentage of positivity in combination of the ELISA methods for ICA and GAD yielded 29.4%, ICA plus IAA showed 38.2%, and GAD plus IAA was 52.9%, respectively. IAA positive rates in two groups divided by the age of 10 showed no significant difference. The presence of the autoantibodies did not influenced the C-peptide level.
CONCLUSIONS
Further large scale studies including prediabetic state and autoimmune diabetes are required to establish the accurate diagnostic method of islet cell autoantibodies. But, presently ELISA method was considered that more improvement was needed for reliable and comparable results especially GADA.