This test is used to evaluate the level of thyroxine T4 produced by the thyroid gland. The level of T4 are increased in the case of hyperthyroidism, thyrotoxicosis and subacute thyroiditis. This test is carried out in combination with T3 and T4 uptake by the binding proteins. This allows the determination of the underlying cause of T4 abnormality, which can be either due to abnormalities in thyroxine-binding protein or overall changes in the function of thyroid.
LabEspy recommends Lab Testing API, Walk-In Lab, Ulta Lab Tests for this test.