What parameter is measured in a Dexamethasone suppression test?

The Dexamethasone suppression test primarily measures cortisol levels in order to assess how the body responds to dexamethasone, a synthetic steroid. A key parameter measured in this test is midnight salivary cortisol.

The rationale behind using midnight salivary cortisol is that cortisol normally follows a diurnal rhythm, with levels peaking in the morning and declining throughout the day. Elevated cortisol levels at night can indicate abnormal adrenal gland function or an overproduction of cortisol, as seen in conditions like Cushing's syndrome. Dexamethasone, when administered, typically suppresses cortisol production in healthy individuals, and the effectiveness of this suppression can be evaluated by checking saliva cortisol levels at midnight.

The other options do not represent the primary parameter of interest in the Dexamethasone suppression test. While 24-hour urinary free cortisol is also used in evaluating conditions related to cortisol abnormalities, it is not the parameter typically monitored during this specific test. Blood glucose levels and aldosterone levels are unrelated to the mechanism of action or purpose of the Dexamethasone suppression test. By evaluating midnight salivary cortisol following dexamethasone administration, clinicians can establish whether cortisol suppression occurs appropriately, aiding in the diagnosis and management of various