Dexamethasone

Dexamethasone is a synthetic potent glucocorticoid that is widely used for the treatment of inflammatory and autoimmune conditions. In normal physiology, dexamethasone administration also results in suppression of the hypothalamic-pituitary-adrenal axis, leading to suppression of cortisol production by the adrenal glands. Dexamethasone suppression testing is therefore an established screening test in the investigation of suspected hypercortisolism (Cushing’s syndrome). The most common variation of the test is known as the overnight dexamethasone-suppression test (ONDST). Measurement of serum dexamethasone along with cortisol during the ONDST is recommended by the Endocrine Society in order to identify false-positive cortisol results (>50 nmol/L). False positive cortisol results can be caused by variations in dexamethasone adsorption and/or metabolism, or by patient non-adherence to the dexamethasone given. Studies have shown that serum dexamethasone concentrations >3.3 nmol/L result in cortisol suppression to ≤50 nmol/L in healthy volunteers.