Cortisol, Free (24-Hour Urine) Unit Converter

Urine free cortisol measures the amount of unbound (free) cortisol excreted in the urine over a 24-hour period. Cortisol is the body's primary stress hormone, a glucocorticoid that regulates metabolism, immune function, blood pressure, and the stress response.

Most cortisol in the blood is bound to proteins such as cortisol-binding globulin (CBG) and albumin. Only a small fraction circulates freely. When cortisol levels exceed the binding capacity of these proteins, the excess free cortisol is filtered by the kidneys and appears in the urine.

Because the test captures total cortisol output across an entire day, it avoids the problems caused by cortisol's natural fluctuations throughout the day and provides a reliable picture of overall cortisol production.

Cortisol is produced in the zona fasciculata, the middle layer of the adrenal cortex in the adrenal glands, which sit on top of each kidney. Its release is controlled by the hypothalamic-pituitary-adrenal (HPA) axis, where the hypothalamus releases CRH, the pituitary releases ACTH, and the adrenal glands respond by producing cortisol.