What is the Origin of Free T Bio-Availability?

This term emerged from endocrinology as researchers sought a more accurate measure of thyroid hormone activity, recognizing that protein binding significantly sequesters the hormone from biological action. 'Bio-availability' denotes the fraction capable of eliciting a physiological response.

What is the Mechanism of Free T Bio-Availability?

The mechanism relies on the dissociation kinetics of the thyroid hormone from its transport proteins within the vascular space. Factors influencing this include SHBG concentration, inflammation, and estrogen status, all of which compete for binding sites. Increasing free T ensures adequate cellular uptake and T3 conversion necessary for mitochondrial function and energy production.

Free T Bio-Availability ∞ Area

Free T Bio-Availability

Meaning

The quantifiable fraction of total circulating thyronine hormones (T3 and T4) that is unbound by plasma proteins like SHBG or TBG, making it immediately available to interact with cellular receptors. High bio-availability correlates directly with downstream thyroid hormone effect and metabolic rate. Clinically, this fraction is far more significant than total T levels.