What is the Origin of Hormone Bioavailability Measurement?

The concept originates in pharmacokinetics and endocrinology, where 'bioavailability' refers to the degree and rate at which an administered substance is absorbed and becomes available at the site of action. Applying this to endogenous hormones distinguishes between the total pool and the physiologically relevant fraction. The development of sensitive assays allowed for this critical distinction in clinical practice.

What is the Mechanism of Hormone Bioavailability Measurement?

Most hormones, particularly steroids, circulate bound to proteins like Sex Hormone-Binding Globulin (SHBG) and albumin; only the free fraction can diffuse into cells. Measurement techniques, such as equilibrium dialysis or calculated free indices, are used to isolate this fraction. A comprehensive assessment requires evaluating not only the free hormone but also the concentration of its binding proteins, as fluctuations in these proteins significantly alter the amount of hormone available to tissues.

Hormone Bioavailability Measurement ∞ Area

Hormone Bioavailability Measurement

Meaning

Hormone bioavailability measurement is the clinical practice of quantifying the fraction of a hormone that is unbound to carrier proteins and therefore biologically active and capable of engaging target cell receptors. Measuring this free, active fraction, rather than the total circulating level, provides a more accurate assessment of a patient’s true hormonal status and tissue exposure. This precision is fundamental for safe and effective hormone replacement therapy titration.