The Complete Thyroid Profile combines the four most clinically useful thyroid function tests, giving a thorough assessment of a patient’s thyroid function.
Thyroid disease or dysfunction can explain a wide variety of symptoms, yet it is notoriously under-diagnosed. Population studies such as the Colorado Thyroid Disease Prevalence Study demonstrate that up to 10% of Americans may have thyroid dysfunction, defined as abnormal levels of thyroid-stimulating hormone (TSH).
Overt hypothyroidism, with its characteristically high TSH and low circulating thyroxine (T4) levels, or hyperthyroidism, with low TSH and high T4 levels (most commonly manifested as Graves’ Disease), are relatively easy to recognize clinically. But an elevated TSH associated with normal thyroid hormone levels, defined as “subclinical” hypothyroidism, is thought to be present in 4-10% of the general population and in up to 20% of women over 60 years old, while a low TSH and normal thyroid hormone levels, or subclinical hyperthyroidism, occurs in about 2% of the population and is most common in women, blacks, and the elderly.
Thyroid hormones are primarily involved in directing the metabolic activity of cells, and a properly regulated thyroid is therefore essential to a wide array of biochemical processes in the body. Subclinical hypo- and hyperthyroidism can therefore result in symptoms even when hormone levels appear to be normal, because the abnormal TSH indicates that there is still a disorder in thyroid regulation, and because thyroid hormone activity can be affected by interactions with other hormone systems, particularly estrogens and cortisol, and by some nutritional deficiencies. Management of thyroid dysfunction requires an understanding of these interactions and careful monitoring of treatment with regular thyroid function tests.
The presence of thyroid peroxidase (TPO) antibodies has been found to help diagnose thyroid disease in patients with abnormal TSH and/or mild thyroid symptoms, and is used to indicate the presence of autoimmune thyroiditis (Hashimoto’s disease, the most common cause of overt hypothyroidism), since 95% of such patients are positive for TPO antibodies.
Symptoms and conditions:
TSH – Thyroid Stimulating 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 result in insufficient TSH being produced to stimulate the thyroid (secondary hypothyroidism).
Free T4 – Thyroxine
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 indicates hyperthyroidism. High TSH and low T4 indicates a thyroid gland disease, such as thyroiditis.
Free T3 – Triiodothyronine
Triiodothyronine is 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 thyroiditis (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.