Saliva vs. blood for testosterone: the honest answer

They do not measure exactly the same thing

Most testosterone in blood is bound to proteins. A much smaller portion is unbound, or free. Testosterone that reaches saliva is often discussed as a proxy for the free fraction, but saliva and serum values are not interchangeable.

Salivary concentrations are much lower, which makes the measurement technically demanding. Collection method, contamination, oral health, storage, assay chemistry, and the time of day can all affect results.

Where the science stands today

The current Endotext laboratory reference says salivary testosterone correlates moderately well with plasma free testosterone and can be useful in research or when blood collection is impractical. It also says salivary assays are not recommended for clinical purposes.

That distinction matters: an assay can be useful for studying within-person patterns before it is suitable for diagnosing a medical condition. Analytical accuracy, repeatability, reference ranges, and agreement with validated comparators all need to be established for the intended use.

What Axis would need to prove

A credible product cannot rely on convenience alone. Development would need to characterize precision across the expected concentration range, lot-to-lot consistency, stability, common interferents, collection variability, and correlation to appropriate laboratory methods.

Until that work is complete, Axis should be understood as an active R&D concept for wellness pattern tracking—not a replacement for the blood tests used to diagnose hypogonadism.

• Repeatability across days and cartridge lots
• Robust collection and interference controls
• Transparent comparison with validated laboratory methods