Diagnostic value of insulin autoantibodies for latent autoimmune diabetes in adults

Abstract

Objective To investigate the diagnostic value of insulin autoantibody(IAA) for latent autoimmune diabetes in adults (LADA). Methods Sera of 1003 phenotypic type 2 diabetes mellitus (T2DM) patients from the Second Xiangya Hospital of Central South University were screened for IAA with micro–plate radioimmuneassay. Autoantibodies to glutamic acid decarboxylase (GADA) and autoantibodies to protein tyrosine phosphatase(IA–2A) were analyzed with radioligand assay. Four patients with IAA positive alone were clinically followed up for 4 years. Comparisons between autoantibody status groups used two–sample t tests, or Wilcoxon signed–rank tests for non–normally distributed data. All statistical tests were performed by SPSS 13.0. Results The positivity rate of IAA (3.39%, 34/1003)in clinic–based, phenotypic T2DM patients was higher than that of healthy controls (0.95%, 3/317)(3.39% vs 0.95%, χ2=5.3, P<0.05), but lower than that of type 1 diabetes mellitus (T1DM) (21.82%, 24/110)(3.39% vs 21.82%, χ2=68.2, P<0.01). The positivity of combining three antibodies was 10.47%(105/1003), higher than 6.58% (66/1003) of GADA alone, 2.79% (28/1003) of IA–2A alone, 3.39% (34/1003) of IAA alone(χ2=9.2, 37.8 and 46.2, respectively, all P<0.05). Combined IAA measurement increased 2.39% of LADA. The IAA positivity decreased year on year during the peroid of follow–up. During that time, 2 out of 4 patients accompanied by GADA. Average descending rate of fasting insulin levels in IAA positive group was 15.37%, compared with 5.29% of its matched group, and without significant difference(t=1.7, P=0.059). Conclusions IAA can be used to screen LADA in penotypic T2DM in Chinese population. Combined IAA, GADA, and IA–2A testing can improve identifying LADA. Key words: Insulin antibodies; Diabete mellitus, type 2; Autoimmune diseases