RBP4 and type 2 diabetes mellitus: A quantitative protein expression profile based on isobaric tagging for relative and absolute quantification (iTRAQ) showed that there were 69 differentially expressed proteins in the plasma of T2DM patients compared with non-diabetic individuals, including a variety of proteins secreted by the liver and related to insulin resistance in diabetic patients, including α 2-macroglobulin, selenoprotein P, retinol binding protein 4 (RBP4) (12).