Triiodothyronine is produced mainly from the deiodination of thyroxine in the peripheral tissues but is also synthesized by and stored in the thyroid gland as an amino acid residue of the protein thyroglobulin. Triiodothyronine circulates in the blood, where it is bound mainly to thyroxine-binding globulin and thyroxine-binding prealbumin. About 99.7% of the T3 found in the blood is attached to protein and the rest is free (unattached). T3 increases the basal metabolic rate and, thus, increases the bodys oxygen and energy consumption. See Triiodothyronine (FT3), Free, Serum; and Thyroxine (FT4), Free, Serum
Indicate T3 total to avoid confusion with free T3.