FT3
Human triiodothyronine (T3) is a thyroid hormone which circulates bound to various proteins. Only 0.3 % of total serum triiodothyronine is not bound to proteins. This free triiodothyronine (FT3) is responsible for biological activity. Its concentration is independent of the concentration of the binding proteins and thus reflects the true thyroid status. The determination of free triiodothyronine is intended to be used as an aid in diagnosis of various thyroid disorders.
