Bridging-type enzyme-linked immunoassay for zinc transporter 8 autoantibody measurements in adult patients with diabetes mellitus

Aims A bridging-type ELISA for measuring autoantibodies to zinc transporter 8 (ZnT8A) was assessed using samples from different forms of diabetes mellitus. Methods ZnT8A were measured using an ELISA in patients with type 1 diabetes mellitus (T1DM; n = 94), latent autoimmune diabetes of adulthood (LADA; n = 51), type 2 diabetes mellitus (T2DM; n = 59) and healthy blood donors (HBD; n = 200). ZnT8A in ELISA and immunoprecipitation assays (IPA) using ZnT8 dimer (W325/R325) and monomers (W325, R325 and Q325) were compared. Results Inter- and intra-assay coefficients of variation (CV) were 7.1% and 1.7%, respectively (medium ZnT8A) and 8.5% and 2.7%, respectively (high ZnT8A). In the ELISA 51/94 (54.3%) T1DM, 16/51 (31.4%) LADA and 1/59 (1.7%) T2DM sera were ZnT8A positive. ROC analysis of T1DM and HBD for the ELISA showed 54% sensitivity and 99% specificity (cutoff 15 u/mL) and AUC 0.80 (95% CI, 0.74–0.86). ELISA and IPA measurements were in very good agreement (r = 0.856, k = 0.889, n = 204). Measurement of ZnT8A in addition to autoantibodies for GAD, IA-2 and insulin increased antibody positivity in T1DM by 4.3%, from 80.9% to 85.1%. Conclusions The bridging-type ELISA is a convenient and reproducible method for determination of ZnT8A in serum. Measurement of ZnT8A increased autoantibody positivity in adult T1DM