A good initial urinary screening test for suspected Cushing's disease is:

A good initial urinary screening test for suspected Cushing's disease is:

• A. Endogenous ACTH
• B. Low-dose dexamethasone suppression test
• C. Cortisol/creatinine ratio
• D. ACTH stimulation

Answer: (C)

A urinary cortisol to creatinine ratio is used because it provides a simple, noninvasive screen that reflects cortisol production over a period of time rather than at a single moment. Normal serum cortisol can be influenced by stress or the time of day, whereas a urine sample normalized to creatinine accounts for how concentrated the urine is and captures daily cortisol output. If the ratio is elevated, it suggests hyperadrenocorticism and prompts further confirmatory testing; if it’s normal, HAC is less likely, potentially avoiding unnecessary additional tests. The other options are more invasive or time-consuming dynamic or stimulation tests and are typically used after screening to confirm a diagnosis or differentiate causes, rather than as initial screening.

A urinary cortisol to creatinine ratio is used because it provides a simple, noninvasive screen that reflects cortisol production over a period of time rather than at a single moment. Normal serum cortisol can be influenced by stress or the time of day, whereas a urine sample normalized to creatinine accounts for how concentrated the urine is and captures daily cortisol output. If the ratio is elevated, it suggests hyperadrenocorticism and prompts further confirmatory testing; if it’s normal, HAC is less likely, potentially avoiding unnecessary additional tests. The other options are more invasive or time-consuming dynamic or stimulation tests and are typically used after screening to confirm a diagnosis or differentiate causes, rather than as initial screening.