Which test is most commonly used as a screening method for Cushing's disease?

The low-dose dexamethasone suppression test is the most commonly used screening method for Cushing's disease. This test assesses the body's response to dexamethasone, a synthetic glucocorticoid. In a healthy individual, administration of dexamethasone should suppress cortisol production by the adrenal glands. However, in patients with Cushing's disease, cortisol levels remain elevated despite the suppression, indicating the presence of excess cortisol production due to an adrenal or pituitary tumor.

This test is preferred because it is relatively simple to administer and interpret, making it a practical initial screening tool in clinical practice. If cortisol levels are elevated after low-dose dexamethasone administration, it raises suspicion for Cushing's syndrome, prompting further diagnostic evaluation to confirm the syndrome and identify its cause.

Other tests like the high-dose dexamethasone suppression test are used later in the diagnostic process, primarily to differentiate between Cushing's disease and other causes of excess cortisol production. The 24-hour urine cortisol level is also a useful diagnostic tool, but it is less commonly used as an initial screening test since it measures total cortisol production over a day rather than assessing suppression. Similarly, salivary cortisol levels provide insight into cortisol secretions