What is the Origin of Free T3 Availability?

This concept evolved from the limitations of measuring total thyroid hormone, recognizing that only the unbound fraction exerts physiological effects.

What is the Mechanism of Free T3 Availability?

Its availability is dynamically regulated by the binding affinity of thyroid-binding globulin (TBG) and the efficiency of the deiodinase enzymes converting T4 to the active T3 form.

Free T3 Availability ∞ Area

Free T3 Availability

Meaning

Free T3 Availability refers to the concentration of unbound, biologically active triiodothyronine circulating in the serum, which is available to enter target tissues.