Corticosteroid-binding globulin (CBG): A plasma glycoprotein that binds cortisol with high affinity, regulating its free concentration and temporal delivery to target tissues.

Serum Concentrations of Estrone, Androstenedione, Testosterone and Sex-hormone-binding Globulin in Postmenopausal Women with Breast Cancer and in Age-matched Controls, Upsala Journal of Medical ...

But most serum cortisol is bound to corticosteroid-binding globulin and albumin, and serum free cortisol (which typically is not measured) is the physiologically active component of total cortisol.