The screen for adrenal cortical hyperfunction with the greatest sensitivity and specificity is which test?

• A. 24 hr. urine free cortisol
• B. plasma cortisol
• C. urinary 17-hydroxycorticosteroids
• D. plasma corticosterone

Answer: (A)

The best screening test for adrenal cortical hyperfunction is the 24-hour urinary free cortisol. This test measures the amount of cortisol excreted in urine over a full day, capturing the unbound (free) portion of cortisol and reflecting overall daily production. It minimizes the effects of diurnal variation and acute stress that can make a single plasma cortisol measurement unreliable, giving it higher sensitivity and specificity for detecting cortisol excess. Other options, like a single plasma cortisol or urinary metabolites, are more affected by timing, stress, or are less specific for sustained hypercortisolism, and thus are not as reliable as the 24-hour urinary free cortisol.