Which Tests are Included in the
Complete Thyroid Profile?
TSH- Thyroid Stimulation Hormone
TSH is produced by the pituitary and acts on the thyroid gland to stimulate production of T4. Higher than normal TSH can indicate a disorder of the thyroid gland, while low TSH can indicate over-production of T4, which acts in a 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- Thyroxin
The predominant hormone produced by the thyroid gland. An inactive hormone, T4 converts to T3 within cells, free T4 is the non-protein-bound fraction of the T4 circulating in the blood, representing about 0.04% of the total circulating T4, which is available to tissues. Low TSH combined with low T4 levels indicates hypothyroidism, while low TSH and high T4 levels indicate hyperthyroidism. High TSH and low T4 indicate a thyroid gland disease, such as thyroiditis.
Free T3- Triiodothyroinine
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.
TPO- Thyroid Peroxidase Antibodies
Thyroid peroxidase is an enzyme used by the thyroid gland in the manufacture of T4. In patients with autoimmune thyroididtis (predominantly Hashimoto’s disease), the body produces antibodies that attack the thyroid gland, and levels of these antibodies in blood can diagnose this condition and indicate the extent of the disease.