Saliva tests and blood tests measure different forms of cortisol and understanding that difference helps explain what each one tells you.

Here's why: Salivary cortisol measures the free, biologically active form of cortisol - the portion that's not bound to proteins and can actually interact with your cells.

Most blood tests, on the other hand, measure total cortisol (both bound and inactive forms together). Since only the free fraction is active in your body, saliva measurements often align more closely with how you're actually feeling and functioning.

Variations in cortisol levels due to timing can also play a critical role. Cortisol follows a diurnal rhythm, peaking about 30 minutes after waking and gradually tapering off as the day progresses. This rhythm means that timing discrepancies between blood and saliva test collections can affect comparisons.

How accurate are saliva tests?

Numerous studies have shown strong correlations between salivary cortisol and the free (active) fraction of cortisol in blood, with correlation coefficients typically ranging from 0.8 to 0.95 — meaning they track together very closely.

While our specific assay hasn't been directly compared to serum cortisol, it has been validated against ELISA (enzyme-linked immunosorbent assay), which is the gold standard laboratory method for measuring salivary cortisol.

ELISA is clinically established and widely accepted in medical research and practice. This validation ensures our test provides accurate and reliable measurements of free cortisol that closely reflect your body's real-time physiological state.

Cortisol levels follow a diurnal rhythm, peaking approximately 30 minutes after waking and tapering as the day progresses. Differences of just 20-30 minutes in sample collection could lead to noticeable differences, emphasizing the importance of consistent timing for accurate interpretation.

A flat cortisol curve with consistently low readings throughout the day can occur for a range of reasons, including irregular sleep patterns, inconsistent morning light exposure, or late caffeine consumption. If you notice a pattern like this, it's worth reviewing your testing conditions and discussing your results with a healthcare provider.