Thyroid Testing

Thyroid hormones directly regulate every cell in our body as most basic functions like metabolism, emotions and thinking. We also test several proteins that affect thyroid function as well as antibodies to thyroid which can detect autoimmunity (when the immune system attacks healthy tissue) and your levels of cortisol, the stress hormone.

The comprehensive thyroid panel includes:

  • Free T3 (Free Triiodothyronine) – the more potent and biologically active thyroid hormone, T3 regulates growth and metabolism throughout the whole body.

  • Free T4 (Free Thyroxine) – considered a precursor hormone, T4 is converted to T3 as required by cells throughout the body; levels of T4 are generally much higher than T3.

  • Total T4 (Total Thyroxine) - Most T4 in the blood is bound to carrier proteins which make it biologically inactive. Total T4 includes unbound (free) T4 plus T4 that is bound to carrier proteins in the blood.

  • rT3 - Reverse T3 (Reverse Triiodothyronine) - As the name implies, Reverse T3 opposes the biological action of T3. It slows metabolism and renders T3 in the body biologically inactive. The rate of rT3 production relative to T3 will increase in times of stress (high cortisol) and in the presence of nutrient deficiencies, inflammation or certain medications.

  • Thyroid Stimulating Hormone (TSH) – produced by the pituitary gland, TSH tells the thyroid gland to increase or decrease production of T4 or conversion to T3 depending on the amounts circulating in the bloodstream via an efficient feedback system.

  • Anti-TG (Antibodies to Thyroglobulin) – a precursor to T4. If Anti-TG are present in significant amounts, this suggests an abnormal immune response against your own body, also called autoimmunity.

  • Anti-TPO (Antibodies to Thyroperoxidase) – is an enzyme that initiates the synthesis of T4. Antibodies to TPO indicate autoimmunity where the body is attacking normal proteins in the blood (in this case, TPO). People with anti-TPO have a higher chance of developing hypothyroidism that those who do not have antibodies to TPO.

  • Tg (Thyroglobulin) – The main function of Tg is to store iodine, which is a necessary nutrient for the production of thyroid hormones T3 and T4. This test is particularly useful when monitored over time versus a single measurement and can sometimes be a useful tumor marker in patients with previous thyroid cancer.

  • TBG (Thyroid Binding Globulin) – is a carrier protein for thyroid hormones so its role is to transport T4 and T3 through the bloodstream. The thyroid gland adjusts to changing levels of TBG in order to keep free T4 constant and it is particularly useful when thyroid (T4) levels do not necessarily correlate with clinical symptoms. TBG levels are largely affected by other hormones and many prescription drugs and is useful in diagnosing the reason behind abnormal thyroid hormone levels.