T3 | Triiodothyronine

Triiodothyronine (T3) is essentially responsible for the development of thyroid hormone effects in various target organs. The concentration of T3 in the serum reflects more the functional state of peripheral tissues than the secretory activity of the thyroid gland. All T3 is produced from T4. The effect of triiodothyronine in the periphery is incomparably stronger than that of thyroxine (T4). When the conversion of T4 to T3 is impaired, the concentration of T3 decreases. This can happen due to the effects of medications, such as propranolol, glucocorticoids, or amiodarone, and when suffering from a severe non-thyroidal illness. T3 determination is used in the diagnosis of T3 thyrotoxicosis, early stages of thyroid function activation, and confirmation of actual thyrotoxicosis diagnosis.