Cortisol A group of hormone called glucocorticoids Plasma Adult 8 a.m-10 a.m: 5-23 µg/dl 4 p.m-6 p.m: 3-13 µg/dl To diagnose Cushing's Syndrome, Cushing's disease, and primary and secondary adrenal insufficiency To distinguish between primary and secondary adrenal insufficiency Stress Acute illness Surgery Trauma Pregnancy Anxiety Exogenous estrogen Starvation Anorexia nervosa Alcoholism Renal failure Addison's disease Hypophysectomy Postpartum pituitary necrosis Pituitary destruction Noncompliance with dietary or activity restrictions With RIA: Androgen, Estrogen, Phenytoin, Hepatic dysfunction, renal failure With competitive protein binding assay: Prednisolone, 6-alpha-methylprednisolone With fluorometric assays: Jaundice, renal failure, medications With high-performance liquid chromatography: Prednisone, prednisolone