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Bioavailable Hormone

Meaning

The Bioavailable Hormone is the fraction of a hormone circulating in the bloodstream that remains unbound to high-affinity carrier proteins, primarily Sex Hormone-Binding Globulin (SHBG), and is therefore physiologically active. This unbound, or free, component represents the true hormonal signal capable of interacting with target cell receptors to elicit a biological response. Clinically, measuring this bioavailable fraction offers a more accurate assessment of a patient’s functional hormonal status than merely evaluating the total hormone concentration. It is the most critical component for understanding endocrine signaling access and functional utility.