Cortisol

The DRG:HYBRiD-XL Cortisol is an enzyme immunoassay for the quantitative in vitro diagnostic measurement of cortisol in serum and plasma.Only for use with the DRG:HYBRiD-XL Analyzer.Cortisol, also known as hydrocortisone, is the principal glucocorticoid produced by the zona fasciculata of the adrenal cortex. Cortisol is synthesized from cholesterol, and is released in the circulation in a pulsatile and circadian pattern with highest levels in the morning that decrease throughout the day and achieve lowest concentration at night (1). Cortisol release is controlled by adrenocorticotropic hormone (ACTH) which is produced in the anterior pituitary. The release of ACTH is controlled by the hypothalamic corticotrophin-releasing hormone (CRH) and by a negative feedback system at both hypothalamic and pituitary levels involving cortisol.(2). Less than 6% of plasma cortisol circulates unbound from transcortin and albumin (3). Only free cortisol binds to specific intracellular receptors, where it promotes gluconeogenesis and deposition of liver glycogen, increases blood glucose (4), and effects fat (5) and bone metabolism (6), renal function (7) and anti-inflammatory immune responses. Cortisol is excreted primarily in urine in an unbound (free) form. Measurement of plasma cortisol levels is useful in diagnosing conditions related to functions of the adrenal cortex, including Cushing’s syndrome (hypercortisolism) (8), Addison’s disease (hypocortisolism) (9) or secondary adrenal insufficiency (hypocortisolism) and adrenal tumors. Abnormal cortisol levels may also be linked to stress (10) prostate cancer, depression and schizophrenia. In many cases, it is necessary to perform dynamic tests (suppression or stimulation) in order to localize the defect at one of the three main levels (i.e. adrenal, pituitary, hypothalamus).Samples should always be withdrawn at a fixed hour (e.g. 8 am).The DRG:HYBRiD-XL Cortisol Kit is a solid phase enzyme-linked immunosorbent assay (ELISA) based on the principle of competitive binding. The antibody coated wells (ACW) of the reagent cartridges are coated with a monoclonal [mouse] antibody directed towards a unique antigenic site of the cortisol molecule. Endogenous cortisol of a patient sample competes with a cortisol-horseradish peroxidase conjugate for binding to the coated antibody. After incubation the unbound conjugate is washed off. The amount of bound peroxidase conjugate is inversely proportional to the concentration of cortisol in the sample. Having added the substrate solution, the intensity of colour developed is inversely proportional to the concentration of cortisol in the patient sample.