Late-night salivary cortisol concentration is used to diagnose which condition?

• A. Cushing disease
• B. Addison disease
• C. Pseudocushing
• D. Hyperthyroidism

Answer: (A)

Late-night salivary cortisol is used to screen for Cushing's syndrome because it tests whether the normal drop in cortisol at night is preserved. In healthy individuals, cortisol levels fall to a low point at night; in Cushing's syndrome the cortisol remains inappropriately elevated, reflecting ongoing autonomous production. Measuring free cortisol in saliva is convenient and mirrors the serum free cortisol, so an elevated late-night value strongly suggests true hypercortisolism, such as might occur with Cushing disease (pituitary ACTH–secreting tumor) or other causes of Cushing’s. This test helps distinguish true hypercortisolism from pseudocushing, where cortisol is not chronically elevated. Addison disease would show low cortisol, not high, and hyperthyroidism is not diagnosed by this test.