FNDC5 and type 2 diabetes mellitus: Therefore, the present study aimed to evaluate serum irisin levels and their associations with key metabolic markers, including indices of insulin resistance and lipid-related risk factors (HOMA-IR, Quantitative Insulin Sensitivity Check Index (QUICKI), TG/HDL-C, AIP, and LAP), in individuals with PreDM and newly diagnosed T2DM.