What does the Free Cortisol test measure?

Why is Free Cortisol measured?

Urinary free cortisol is a first-line screening test for endogenous Cushing syndrome, particularly when day-to-day variability is high. It is also monitored in patients with suspected adrenal insufficiency or those on supraphysiological glucocorticoid therapy, and serves as a functional index of hypothalamic–pituitary–adrenal axis output over 24 hours.

Reference ranges

Standard reference

Laboratory-specific; typically 20–90 µg/24 h for adults.

Functional medicine optimal

Functional practitioners may interpret mid-range values as optimal, though this approach is not standardised; clinical endocrinology relies on laboratory reference intervals derived from healthy populations.

Units

µg/24 h, nmol/24 h

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.