Thyroid Panel (TSH, T4, Free T4, Free T3)
This panel is used to evaluate thyroid function. The combination of the serum T4 and T3 uptake (THBR) as an indirect assessment of thyroxine-binding globulin (TBG). TBG helps to determine whether an abnormal T4 value is due to alterations in serum thyroxine-binding globulin or to changes of thyroid hormone levels. Deviations of both tests in the same direction usually indicate that an abnormal T4 is due to abnormalities in thyroid hormone. Deviations of the two tests in opposite directions provide evidence that an abnormal T4 may relate to alterations in TBG. This panel consists of the following tests: Thyroid-Stimulating Hormone (TSH), Thyroxine (T4), Free Thyroxine (T4), Free Tri-iodothyronine (T3):
- Thyroid-Stimulating Hormone (TSH)
This test is used to identify primary hypothyroidism and to differentiate it from secondary (pituitary) and tertiary (hypothalamus) hypothyroidism.
- Thyroxine (T4)
This test is used to evaluate thyroid function. T4 is decreased in hypothyroidism and in the third stage of subacute thyroiditis. T4 is increased with hyperthyroidism, subacute thyroiditis in its first stage and with thyrotoxicosis due to Hashimoto disease. T4 is also used to diagnose toxicosis.
- Thyroxine (T4) Free, Direct
This test is used to evaluate thyroid function in individuals who may have protein abnormalities that could affect total T4 levels. It is used to evaluate thyroid function and monitor replacement and suppressive therapy.
- Tri-iodothyronine (T3), Free, Serum
This test is used to evaluate thyroid function. It is primarily used to diagnose hyperthyroidism. It is also used to assess abnormal binding protein disorders and to monitor thyroid replacement and suppressive therapy
