What does the Salivary Cortisol — Midday test measure?

Why is Salivary Cortisol — Midday measured?

The noon salivary cortisol provides the first reference point for assessing the rate and trajectory of the diurnal cortisol decline — the pattern between morning and noon is the steepest physiological slope in the cortisol diurnal curve. In functional and integrative medicine, this time point is interpreted as part of the diurnal rhythm pattern rather than in isolation. Elevated noon cortisol alongside elevated morning cortisol indicates sustained HPA axis hyperactivation — consistent with chronic psychological stress, active inflammatory disease, or hypothalamic dysregulation. Suppressed noon cortisol in a patient with fatigue and midday energy collapse suggests early diurnal cortisol insufficiency despite potentially preserved morning output.

Reference ranges

Standard reference

1.2–3.0 ng/mL (3.3–8.3 nmol/L) # REVIEWER FLAG: Confirm Genova Diagnostics reference range and collection window for noon salivary cortisol — typically collected between 11:00 and 13:00 hours. Values reflect the post-CAR decline phase of the diurnal curve.

Functional medicine optimal

1.5–2.5 ng/mL (functional medicine optimal for a healthy diurnal cortisol decline trajectory). # REVIEWER FLAG: Functional optimal not standardised — reviewer to confirm.

Units

ng/mL, nmol/L

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