What is the Origin of Bioavailable Testosterone Index?

The concept emerged from the need to accurately assess androgen deficiency, recognizing that total testosterone measurements often fail to reflect true biological activity due to varying levels of binding proteins. The term index signifies a ratio or calculation used as a clinical marker, combining the concepts of biological availability and the hormone's primary role.

What is the Mechanism of Bioavailable Testosterone Index?

The index is mathematically derived, typically involving the measured concentrations of total testosterone, SHBG, and albumin in a blood sample. The calculation accounts for the differential binding affinities, where testosterone bound to albumin is considered readily dissociable and therefore bioavailable for cellular action. This mechanism provides clinicians with a precise tool for diagnosing conditions like hypogonadism, guiding hormonal optimization strategies, and monitoring treatment efficacy.

Bioavailable Testosterone Index

Meaning

The Bioavailable Testosterone Index is a calculated value used in clinical endocrinology to estimate the amount of testosterone that is freely available to interact with target tissues. This fraction includes both free testosterone and testosterone loosely bound to albumin, excluding the hormone tightly bound to Sex Hormone-Binding Globulin (SHBG). It offers a more clinically relevant measure of androgen status than total testosterone alone, particularly when SHBG levels are abnormal.