Comparison of two insulin assays for first-phase insulin release in type 1 diabetes prediction and prevention studies

► Low first-phase insulin release (FPIR) is important to type 1 diabetes prediction and prevention studies. ► The reference standard for FPIR uses an insulin radioimmunoassay (RIA). ► We compared FPIRs by the insulin RIA to a more specific, faster insulin immunoenzymometric assay (IEMA). ► The insulin IEMA accurately classified FPIRs compared to RIA-based FPIRs in 68% of subjects. ► FPIR by the less practical insulin RIA can be limited to subjects at risk for type 1 diabetes with an uncertain FPIR by an insulin IEMA.