Saliva testing measures the hormones that are bioavailable at the tissue, available for absorption so they can create a hormonal response.
Blood (serum) testing measures the total level of a specific hormone in the bloodstream, not the bioavailable level. Hormones are partially bound to a protein as they travel through the bloodstream, and are not free to reach the tissue and create a hormonal response.
*It is very important to measure the amount that is bioavailable.
Serum vs. Saliva:
“With saliva measuring the bioavailable (non-protein-bound) fraction of circulating hormones that can freely diffuse into tissues, it provides a more accurate assessment of topical hormone supplementation than serum. Serum levels do not rise significantly after topical dosing. By contrast, saliva levels do — reflecting tissue delivery of the topically delivered hormone.”
Source: Accurate Hormone Testing for Different Supplementation Types

