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Bioactive Hormone Availability

Meaning

Bioactive hormone availability quantifies the fraction of a specific circulating hormone that is unbound to plasma proteins and therefore physiologically active, capable of eliciting a response at target cell receptors. This measurement is clinically significant because only the free, unbound hormone can diffuse across capillary walls and interact with cellular targets to regulate physiological processes. Understanding this available fraction is crucial for accurately assessing true hormonal status, particularly for steroid hormones like testosterone and estradiol, which are largely protein-bound. The total hormone concentration alone often misrepresents the functional endocrine signal.