Interlaboratory Evaluation of Multiplex Autoantibody Assay Performance in the Islet Autoantibody Standardization Program 2024 Workshop

Objective: The Islet Autoantibody Standardization Program (IASP) evaluates type 1 diabetes autoantibody assays through international interlaboratory comparison studies. This report describes 2024 IASP workshop results for multiplex assays that simultaneously measure multiple islet autoantibodies, increasingly adopted for population screening programs. Research Design and Methods: Participating laboratories analyzed coded sera from new-onset type 1 diabetes individuals (n=50), diabetes-free blood donors (n=98), and replicate samples (n=3). Performance was assessed using sensitivity, specificity, adjusted sensitivity at 95%, 99%, and 100% specificity (AS95, AS99, AS100), receiver operating characteristic curve analysis (ROC-AUC), and partial ROC-AUC at 95% specificity (pAUC95). Results: Fifteen laboratories contributed results from 19 multiplex assays using five formats: antibody-dependent agglutination PCR (ADAP, n=6), bridge-ELISA (n=8), electrochemiluminescence (ECL, n=2), luciferase immunoprecipitation system (LIPS, n=1), and protein A luciferase/solid-phase capture LIPS (PAL/scLIPS, n=2). Median ROC-AUC was 0.98 across all platforms, with pAUC95 of 0.048 against a theoretical maximum of 0.05. Laboratory-reported sensitivity ranged 86-96% with specificity 81-100%. Standardized AS99 thresholds eliminated most false positives without compromising sensitivity, achieving 93-97% adjusted sensitivity. Bridge-ELISA platforms demonstrated potential for universal cutoff standardization, while ADAP showed substantial inter-laboratory threshold variation. Conclusions: Multiplex assays demonstrated good overall performance for detecting islet autoantibodies and discriminating cases from controls. However, inter-laboratory variability and platform-specific recognition patterns necessitate further standardization efforts. While not directly tested in this workshop, the results suggest that sequential testing strategies using complementary platforms may be necessary to achieve the stringent specificity required when these assays are used in a screening context.