Unlike blood-based tests, saliva diagnostics can measure the amount of free, unbound hormone that is available to act on the target tissue.
About 95-99% of steroid hormones circulating in the bloodstream are bound to carrier proteins. Saliva contains unbound, bioavailable hormones. Therefore, salivary concentrations better represent circulating levels of free hormones, which are likely to affect the body and be responsible for symptoms related to excessive or deficient hormone levels.