Which laboratory finding is diagnostic for hypercortisolism?

Which laboratory finding is diagnostic for hypercortisolism?

• A. 24-hour urine-free cortisol
• B. Serum ACTH
• C. Plasma renin
• D. Serum aldosterone

Answer: (A)

Hypercortisolism is diagnosed by showing that cortisol production is truly elevated over a period of time. The most direct and reliable way to do this is by measuring how much cortisol is excreted in the urine over 24 hours. The 24-hour urine-free cortisol test captures total daily cortisol output and minimizes the influence of short-term fluctuations or stress, so a persistently high value strongly supports hypercortisolism. Serum ACTH, while helpful for distinguishing ACTH-dependent from ACTH-independent causes once hypercortisolism is established, does not by itself prove that cortisol is in excess. Plasma renin and serum aldosterone are hormones related to the renin–angiotensin–aldosterone system and are used to evaluate disorders of mineralocorticoid excess or deficiency, not cortisol excess.

Hypercortisolism is diagnosed by showing that cortisol production is truly elevated over a period of time. The most direct and reliable way to do this is by measuring how much cortisol is excreted in the urine over 24 hours. The 24-hour urine-free cortisol test captures total daily cortisol output and minimizes the influence of short-term fluctuations or stress, so a persistently high value strongly supports hypercortisolism.

Serum ACTH, while helpful for distinguishing ACTH-dependent from ACTH-independent causes once hypercortisolism is established, does not by itself prove that cortisol is in excess. Plasma renin and serum aldosterone are hormones related to the renin–angiotensin–aldosterone system and are used to evaluate disorders of mineralocorticoid excess or deficiency, not cortisol excess.