Identifying insulin autoantibodies with differential risk in type 1 diabetes with a novel bridging ELISA assay

Insulin autoantibodies (IAA) are commonly measured by radio-binding assays, which detect both high and low affinity binding. Improved assays that preferentially detect high-affinity IAA are likely to provide greater specificity and thereby increase the diagnostic accuracy of IAA for early-stage type 1 diabetes (T1D). This study aimed to develop and validate a novel bridging ELISA for IAA detection. The bridging ELISA detects IAA by their bivalent cross-linking two proinsulin moieties in fluid phase. Validation was performed by using samples from 227 patients with newly diagnosed stage 3 T1D and 1,021 control subjects. Additionally, 202 children positive for IAA by RBA from the general population screening were tested by the bridging ELISA and electrochemiluminescence (ECL) assays. At 99.5% specificity, ELISA detected IAA in 65.2% of patients with stage 3 T1D versus 60.8% by RBA. Among children identified as RBA-positive IAA in general population screening, 80.3% of those with multiple islet autoantibodies and 48.1% of those with single IAA were ELISA-IAA positive (P < 0.0001). For children with single IAA by RBA, ELISA detected 78.9% of ECL-IAA-positive cases versus 27.9% of ECL-IAA negative cases (P < 0.0001). Samples IAA negative by ELISA showed lower antibody affinity. The ELISA IAA assay demonstrates high sensitivity and specificity and could become a practical tool for T1D population screening and clinical diagnosis across laboratories.