Credit: https://www.labrix.com/SalivaryHormoneTesting
Saliva testing measures the bioavailable hormone – the clinically relevant portion delivered to the receptors in the tissues of the body.
Salivary hormone levels are expected to be much lower than serum levels, as only the unbound hormones are being measured. When healthcare providers measure serum hormone levels and prescribe hormone replacement therapy based on those results, patients are often overdosed. If the patients are then tested using saliva, the results are extraordinarily high and create confusion resulting from a lack of correlation between the two methods.
This discrepancy becomes especially important when monitoring topical, or transdermal, hormone therapy. Studies show that this method of delivery results in increased tissue hormone levels (thus measurable in saliva), but no parallel increase in serum levels. Therefore, serum testing cannot be used to monitor topical hormone therapy.
Saliva measures the “unbound” biologically active or free hormone levels in the body:
When blood is filtered through the salivary glands, the bound hormone components are too large to pass through the cell membranes of the salivary glands. Only the unbound hormones pass through and into the saliva. What is measured in the saliva is considered the “free”, or bioavailable hormone, that which will be delivered to the receptors in the tissues of the body.
Serum measures the “protein bound” biologically inactive hormone levels in the body:
In order for steroid hormones to be detected in serum, they must be bound to circulating proteins. In this bound state, they are unable to fit into receptors in the body, and therefore will not be delivered to tissues. They are considered inactive, or non-bioavailable.
Only saliva testing measures topically dosed hormones:
The discrepancy between free and protein bound hormones becomes especially important when monitoring topical, or transdermal, hormone therapy. Studies show that this method of delivery results in increased tissue hormone levels (thus measurable in saliva), but no parallel increase in serum levels. Therefore, serum testing cannot be used to monitor topical hormone therapy.