What is the Origin of Free Hormone Index Calculation?

This index originated in clinical endocrinology as a practical and cost-effective alternative to direct measurement of free hormone levels, which can be technically challenging. The underlying principle is derived from the law of mass action, modeling the equilibrium between bound and unbound hormone fractions in the circulation. It is a standard tool for diagnosing and monitoring endocrine disorders.

What is the Mechanism of Free Hormone Index Calculation?

The calculation relies on the inverse relationship between the concentration of binding protein and the free hormone fraction. For example, a high SHBG level sequesters more testosterone, thereby reducing the free, active hormone, even if total testosterone remains within the reference range. The index provides a critical measure of the functional hormonal status, which is often more clinically relevant than the total concentration alone.

Free Hormone Index Calculation ∞ Area

Free Hormone Index Calculation

Meaning

The Free Hormone Index Calculation is an indirect biochemical method used to estimate the biologically active fraction of a hormone, typically testosterone or thyroxine, that is not bound to plasma transport proteins like Sex Hormone-Binding Globulin (SHBG) or Thyroxine-Binding Globulin (TBG). This calculation utilizes the total hormone concentration and the concentration of its primary binding protein to provide a more accurate proxy for the hormone’s effective bioavailability at the cellular level. The free fraction is the portion capable of diffusing into tissues and binding to intracellular receptors.