Free Thyroxine (FT4): T4 is the most abundant thyroid hormone in the blood. However, only about 1% of T4 in the blood is freely available for use by cells, the rest is bound to a protein. A FT4 test measures the amount of T4 that is biologically active in the blood and can exert an effect on bodily functions.
Triiodothyronine (FT3): T3 is thought to be responsible for most, if not all of the effects of thyroid hormones. About 20% of T3 in the blood is secreted by the thyroid gland, with the remainder being produced by the conversion of T4 in cells around the body. Like T4, most of the T3 molecules in the blood are bound to a protein and only a very small fraction is freely available and biologically active.
Thyroid-Stimulating Hormone (TSH) is produced by the pituitary gland and is responsible for regulation of the secretion of T3 and T4 from the thyroid gland.
Only available in the Advanced Thyroid Function Test.
Anti-TPO is a type of autoantibody. Autoantibodies are produced by the immune system, and are similar to antibodies which are produced against viruses and bacteria, but instead of outside invaders, autoantibodies target the body itself. In this instance anti-TPO targets thyroid peroxidase (TPO) - an enzyme found in the thyroid gland, needed for the production of thyroid hormones.