In this study, we analyzed plasma IL-21, as well as levels of other key pro-inflammatory cytokines (IL-17A, TNF-α and IL-6) with the ultrasensitive Quanterix SiMoA technology at different stages of T1D development, utilizing samples from cross-sectional cohorts of adults with established T1D, children with newly diagnosed T1D, and AAb+ at-risk children together with age-matched controls. Here, TNF is linked to type 1 diabetes mellitus.