R&D Systems now offers a human Retinol-binding Protein 4 (RBP4) Quantikine ELISA (Catalog # DRB400 ). RBP4 binds to and transports retinol (vitamin A) from the liver to the peripheral tissues. RBP4 also promotes hyperglycemia through downregulation of the glucose transporter GLUT4 in adipocytes, the upregulation of the hepatic gluconeogenic enzyme PEPCK, and the attenuation of insulin receptor signaling in skeletal muscle. Serum RBP4 levels are also reported elevated in type 2 diabetes and obesity. This new ELISA is designed to measure RBP4 concentrations in cell culture supernatant, serum, plasma, urine, and saliva.