TSH – Thyroid Stimulating Hormone
Produced by the pituitary, TSH acts on the thyroid gland to stimulate the production of the thyroid hormones T4 and T3. Higher than normal TSH can indicate a disorder of the thyroid gland, while low TSH can indicate over-production of, or excessive supplementation with, T4 and/or T3, which acts in negative feedback on the pituitary to reduce TSH production. Low TSH can also be caused by problems in the pituitary gland itself, which results in insufficient TSH being produced to stimulate the thyroid (secondary hypothyroidism).
Free T4 – Thyroxine                                       Â
T4 (thyroxine) is the predominant hormone produced by the thyroid gland. It is an inactive hormone and is converted to its active form, T3 within cells. Free T4 is the non-bound fraction of the total T4 circulating in the blood. Free T4 is available to the issues and represents 0.04% of the total T4 levels. High TSH combined with low free T4 levels indicates hypothyroidism while low TSH and high free T4 levels indicate hyperthyroidism.
Free T3 – Triiodothyronine
The active thyroid hormone that regulates the metabolic activity of cells. Free T3 is the non-protein-bound fraction circulating in the blood, representing about 0.4% of the total circulating T3, which is available to tissues. Elevated T3 levels are seen in hyperthyroid patients, but levels can be normal in hypothyroid patients because it does not represent the intracellular conversion of T4 to T3, which comprises about 60% of all T3 formed in tissues.
TPOab – Thyroid Peroxidase Antibodies
Thyroid peroxidase is an enzyme used by the thyroid gland in the manufacture of thyroid hormones by liberating iodine for attachment to tyrosine residues on thyroglobulin. In patients with autoimmune thyroiditis (predominantly Hashimoto’s disease), the body produces antibodies that attack the thyroid gland, and levels of these antibodies in the blood can diagnose this condition and indicate the extent of the disease.
