What tests are included in the diagnostic workup for Cushing's syndrome?

The diagnostic workup for Cushing's syndrome primarily focuses on assessing cortisol levels in the body and understanding whether cortisol production is appropriately regulated. The choice that includes urine free cortisol testing and dexamethasone suppression tests is crucial because these tests are integral to confirming the hypercortisolism that characterizes the syndrome.

Urine free cortisol testing measures the cortisol levels excreted over 24 hours and is a reliable indicator of cortisol secretion. Elevated concentrations in urine help to indicate the presence of excess cortisol, supporting the diagnosis of Cushing's syndrome.

The dexamethasone suppression test evaluates how the hypothalamic-pituitary-adrenal (HPA) axis responds to dexamethasone, a synthetic glucocorticoid. In healthy individuals, dexamethasone administration suppresses adrenocorticotropic hormone (ACTH) release, leading to decreased cortisol production. However, in cases of Cushing's syndrome—especially those caused by adrenal adenomas or ectopic ACTH production—this suppression does not occur, confirming the pathology.

The other choices do not encompass the key tests necessary for diagnosing Cushing's syndrome. Options involving thyroid function tests and electrolyte panels may have relevance in the broader context of evaluating a