Midnight salivary cortisol in primary hypercortisolism is typically what?

• A. High
• B. Normal
• C. Low
• D. Very low

Answer: (A)

Cortisol has a circadian rhythm, being low at midnight in healthy individuals. In primary hypercortisolism, this night-time drop is lost and free cortisol remains elevated. Midnight salivary cortisol reflects the circulating free cortisol, so a high value is typical in hypercortisolism. This makes a high midnight cortisol a useful clue pointing toward Cushing’s syndrome, whereas normal or low levels would argue against it.