Which tests constitute screening for Cushing syndrome?

• A. Low-Dose Dexamethasone Suppression Test.
• B. 24 Hr Urinary Free Cortisol Levels.
• C. Salivary Cortisol Levels.
• D. All of the above.

Answer: (D)

Screening for Cushing syndrome relies on tests that detect excess cortisol through different angles of regulation. The overnight low-dose dexamethasone suppression test assesses whether dexamethasone can suppress cortisol production; failure to suppress suggests Cushing. The 24-hour urinary free cortisol captures total daily cortisol excretion; elevated levels indicate hypercortisolism. The late-night salivary cortisol measurement looks at the diurnal rhythm, which is blunted or absent in Cushing, so higher late-night levels point toward the disorder. Because each test has limitations and false positives or negatives can occur, using multiple screening methods increases sensitivity. Therefore, all of these tests can be used for screening Cushing syndrome.