Total T4(Thyroxine)

A thyroid hormone, Thyroxine also known as T4 effects almost every physiological process in the body including growth and development,metabolism,body temperature and heart rate.Production of T3 and its prohormone Thyroxine T4 is activated by Thyroid Stimulating Hormone (TSH) released from anterior pituitary gland. It is a loop feedback process so that if T3, T4 hormone blood levels increase, TSH levels decrease. If the levels drop, TSH will increase to stimulate the production of these target hormones to bring them back to the normal blood levels.
T3 is the true hormone affecting the target tissues and it is approximately four times potent than that of T4.The amount of T4 is higher as 80% where T3 is 20%. T3 is produced from T4 by a transformation on the molecule. The half life of T3 is shorter than that of T4. They circulate in blood by binding to a protein (Tyroxine binding globulin and albumin).
Interpretation:Thyroid tests are performed in a panel manner. These are T3, T4 and the regulating TSH hormone released from the pituitary gland by the stimulation of TRH (Thyroid Releasing Hormone) from the hypotalamus. This happens when the levels of the T3, T4 hormones synthesized in the thyroid gland fall(hypothyroidism) or rise(hyperthyroidism), depending on the type of the thyroid disease. This is called the feedback mechanism (if target hormones rise TSH and TRH decrease, if the target hormones decrease than TSH and TRH rise to stimulate the synthesis in the thyroid gland) A thyroid disorder can cause a wide range of symptoms. The doctor diagnoses and treats the disease according to the symptoms and results of these hormone tests.
Sample: Arm vein blood. Nonfasting
Working day: Everyday
Result Time: Same day 6:00 PM