Comparison of immunoassays for the detection of anti-GAD65 autoantibodies in patients with diabetes mellitus

Abstract

Recent studies have demonstrated that a combination of GAD-antibody assays and IA-2 autoantibody assays show a high diagnostic specificity for Type 1 diabetes. For this reason there is increasing interest in the use of GAD-antibody measurement for Type 1 risk assessment. Since a number of different assays have been published and documented in the literature, the aim of this study was to evaluate four different anti-GAD test systems that are commercially available in Germany. We tested the anti-GAD prevalences in five patient groups with the different immunoassays and compared them with the values obtained by an immunoprecipitation test (IP-Test). All assays correlated well with the IP-test and showed high sensitivity and specificity in the group of patients with recent onset Type 1 diabetes and the control group. The groups tested consisted of 20 subjects with recent onset Type 1 diabetes (< 6 weeks) (sensitivity 70-90%), nine subjects with a Type 1 duration of more than 2 years (sensitivity 11-33%), 21 patients with pluriglandular insufficiency (sensitivity 28.5-47.5%), 10 patients with Type 2 (specificity: 90-100%), and 14 healthy control subjects (specificity: 93-100%). Our data show a high level of sensitivity and specificity of the tested, commercially available, assays. Since almost every laboratory should be able to establish one of these assays, this may facilitate the possibility of further large scale population studies with the aim of investigating GAD-antibody prevalences in screening for Type 1 diabetes. Increased measurement of the diabetes-associated antibodies will be helpful in the differential diagnosis of gestational diabetes mellitus (GDM) and latent autoimmune diabetes of the adult (LADA).