Thyroid dysfunction can explain a wide variety of symptoms because of the central role of thyroid hormones in directing the metabolic activity of cells. The essential thyroid profile accesses the overall thyroid health, which includes checking for hypothyroidism and hyperthyroidism, determines Free T3 and Free T4 levels, monitors dosages for thyroid replacement and tests for autoimmune thyroid disease.
The Essential Thyroid Blood Spot Profile includes TSH, Free T4, Free T3, TPOab, Total T4, and Tgbn.
This profile is recommended for individuals that require:
- Assessing iodine status
- Routine thyroid screening
- Total thyroxine production by the thyroid
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
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.
Thyroglobulin
A protein which is rich in tyrosine and synthesized only in the thyroid gland. When bound to iodine, tyrosine residues in thyroglobulin become the source material for the synthesis of the thyroid hormones T3 and T4. When iodine levels are low, high levels of thyroglobulin can be found in the blood as iodine-poor thyroglobulin builds up and leaks from the thyroid into the bloodstream. Levels of thyroglobulin are an indicator of a person’s average iodine exposure over a period of weeks: the greater the iodine exposure, the lower the thyroglobulin level. An elevated thyroglobulin, in the absence of more serious thyroid diseases such as thyroid cancer, which results in very high blood thyroglobulin levels, indicates low iodine status.
Total T4 – Thyroxine
Total T4 includes both free T4 and protein-bound T4, and therefore represents the thyroid gland’s capacity to synthesize, process, and release T4 into the bloodstream. In contrast, free T4 represents only the circulating hormone that is bioavailable and not tightly complexed with thyroid-binding globulin (TBG). Certain conditions, like oral estrogen usage or pregnancy, can cause total levels to change due to liver-induction of TBG. This can result in no change in free T4 or lower bioavailable levels of free T4, even though total T4 increases.
