What is the Origin of Steroid Hormone Bioavailability?

This term arises because most circulating steroid hormones are lipophilic and require binding to carrier proteins like SHBG or albumin for transport in the aqueous plasma. Recognizing that binding capacity varies significantly among individuals necessitated a focus on the free hormone level as the true indicator of endocrine status. It is a refinement of basic hormone measurement.

What is the Mechanism of Steroid Hormone Bioavailability?

Bioavailability is mechanistically governed by the concentration and binding affinity of SHBG and corticosteroid-binding globulin (CBG), which are themselves regulated by factors like thyroid status and liver function. A change in the concentration of these binding proteins directly alters the equilibrium, shifting the amount of active hormone available to diffuse into target cells and initiate genomic or non-genomic signaling.

Steroid Hormone Bioavailability ∞ Area

Steroid Hormone Bioavailability

Meaning

Steroid Hormone Bioavailability defines the fraction of administered or endogenously produced steroid hormones, such as testosterone or cortisol, that is unbound to plasma proteins and thus free to interact with intracellular receptors to exert a biological effect. Only this unbound fraction is functionally active in target tissues, making it a critical measure of endocrine potential. It separates mere presence from actual physiological impact.