24-hour urine free cortisol testing is used to diagnose which condition?

• A. Cushing disease
• B. Addison disease
• C. Pheochromocytoma
• D. Acromegaly

Answer: (A)

Measuring 24-hour urinary free cortisol looks for cortisol that’s produced over an entire day, capturing hypercortisolism that a single test might miss. When this urinary cortisol is elevated, it points to Cushing syndrome as the cause of excess cortisol. Addison disease would show low cortisol rather than high; pheochromocytoma involves catecholamines, not cortisol; acromegaly stems from excess growth hormone. So this test is used to identify Cushing syndrome, with Cushing disease (the pituitary-related form) being the specific context in many cases. If the result is high, further tests are done to pinpoint the exact source, such as ACTH measurement and follow-up suppression or stimulation tests to distinguish pituitary from adrenal or ectopic causes.