What does the Salivary Cortisol, Diurnal Profile (multiple timed collections across the day) test measure?

Why is Salivary Cortisol, Diurnal Profile (multiple timed collections across the day) measured?

Salivary cortisol has one clearly validated and guideline-endorsed application: late-night salivary cortisol is an established first-line screening test for Cushing's syndrome, where loss of the normal evening nadir is the diagnostic signal. Its independence from binding globulin also makes it useful where corticosteroid binding globulin is altered, as in oestrogen therapy or pregnancy. The broader use of a multi-point diurnal curve to characterise 'HPA axis dysfunction' or to diagnose 'adrenal fatigue' is not clinically validated: the pattern shows wide intra-individual and day-to-day variability, no validated diagnostic thresholds exist for these interpretations, and the concept of adrenal fatigue is not recognised by mainstream endocrinology. Critically, this panel does not diagnose or exclude adrenal insufficiency, which requires morning serum cortisol and ACTH stimulation testing.

Reference ranges

Standard reference

Time-point-specific: highest on waking, declining through the day to a low at night. Per-time-point reference intervals # REVIEWER FLAG: Time-point intervals are assay-/laboratory-specific — confirm ZRT ranges before publication.

Functional medicine optimal

No validated functional optimal diurnal pattern exists; 'optimal' curve shapes cited in functional practice are not supported by diagnostic validation or outcome evidence

Units

nmol/L, µg/dL, ng/mL

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