Bioavailable Hormone Indexing is the clinical assessment and subsequent interpretation of the fraction of a hormone that is unbound to carrier proteins, such as sex hormone-binding globulin (SHBG) or albumin. This index provides a more accurate representation of the hormone’s biological activity at the tissue level compared to measuring total hormone concentration alone. Clinicians use this metric to gauge the true physiological impact of key hormones like testosterone and estrogen. Accurate indexing is paramount for effective and personalized hormonal health management.
Origin
The foundation of this concept lies in the physical chemistry of hormone transport and action, recognizing that only the free, unbound fraction can readily diffuse into target cells to exert its effects. The term ‘indexing’ reflects the analytical method used to calculate or directly measure this specific, active portion. This clinical refinement arose from the limitations observed when total hormone levels did not correlate well with a patient’s clinical presentation or symptoms.
Mechanism
The mechanism is based on the equilibrium between bound and unbound hormone fractions in the circulation. Hormones are synthesized and then largely bind to carrier proteins, which serve as reservoirs and regulate tissue access. Bioavailable Hormone Indexing quantifies the portion not tightly bound, which is the fraction free to interact with cellular receptors and initiate a biological response. Changes in carrier protein concentration, often influenced by liver function or other hormones, directly impact this index, making it a critical measure of hormonal efficacy.
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