Thyroid hormones are T3 and T4 are produced by thyroid gland. Thyroid gland is located in front of the neck under the Adam’s apple. Thyroid gland produces 2 thyroid hormones as; T3- triiodothyronie and T4-thyroxine.
Thyroid hormones affect all of the body and regulates your metabolism. Thyroid hormones have so many effects on body functions like; regulating body temperature, energy production, carbohydrate metabolism, blood pressure, heart rate.
Thyroid hormones bind proteins like albumin and globulin in your body and a little amount of T3 and T4 are found unbound. These unbound form is called free T3 and free T4.
Free T3 ( fT3) is the active form of the T3 thyroid hormone. All of the T3 amount in your body is called total T3.
Free T3 reference range
Purpose of free T3 blood test
Free T3 blood test is preferred to total T3 test because total T3 amount may be affected by several factors. For exp. ; If your albumin value is low, your total thyroid hormone amount may be found low too. Free T3 value is not affected by this type of factors and may provide more information about thyroid gland functions.
T3 is the active form of the thyroid hormones, T4 is transformed to T3 in tissues. 20% of the total T3 is produced in thyroid gland and the rest part is produced in tissues by transforming T4.