The low-dose dexamethasone suppression test is used to distinguish Cushing's syndrome from which group?

• A. Healthy individuals
• B. Ectopic Cushing
• C. Adrenal hyperplasia
• D. Primary hypercorticolism

Answer: (A)

The test relies on negative feedback: in healthy individuals, a low dose of dexamethasone suppresses ACTH from the pituitary, reducing cortisol production. In Cushing’s syndrome, cortisol is produced autonomously and does not get suppressed, so levels remain high after the test. That difference lets clinicians separate true Cushing’s syndrome from normal, healthy individuals. The other options refer to various forms or causes of Cushing’s syndrome, which would also show non-suppression, so they aren’t what this test is designed to distinguish from.