Urinary free cortisol (24h)
What it measures, and what changes the number.
This test measures free, unbound cortisol in urine pooled over a full day. Cortisol is an adrenal steroid hormone whose level rises and falls through the day, so collecting all urine over a day smooths out that rhythm. This line reports the concentration of cortisol in the pooled urine.
It is read alongside the total urine volume for the same collection, because concentration multiplied by volume gives total daily excretion. Urine creatinine is often measured to check the collection was complete, and blood cortisol and ACTH add context.
Missing even one void, or collecting for longer or shorter than a day, changes the result. Some labs ask for the container to be kept cool. The assay matters too: immunoassays and mass spectrometry can give different numbers. Reports may list it as Cortisol libre en orina de 24 horas (concentración).
Often read alongside: Urinary free cortisol, Urine volume (24h), Cortisol, ACTH, Creatinine