Thyroid Stimulating Hormone (TSH) is produced in the pituitary gland and stimulates the thyroid gland to produce thyroid hormones thyroxine (T4) and triiodothyronine (T3).
High levels of TSH indicate an underactive thyroid while low levels indicate an overactive thyroid. In primary pituitary failure, a low TSH will be associated with an underactive thyroid.
Thyroxine (T4) is one of two hormones produced by the thyroid gland. Most T4 is bound to carrier proteins in the blood. This test measures the level of T4 which is free, or unbound, circulating in your blood.
High levels of free thyroxine can indicate an overactive thyroid while low levels can indicate an underactive thyroid.
T4 (Thyroxine) is the main hormone produced by the thyroid gland. T4 is not biologically active, and must be converted to T3 before it can become active in regulating metabolism. Some T4 is bound to proteins, while some T4 is 'free' or unbound. This test measures the level of total T4 in your blood.
Raised T4 can indicate an overactive thyroid while low T4 may indicate that the thyroid is struggling to produce sufficient thyroid hormones.
Triiodothyronine (T3) is one of two thyroid hormones produced by the thyroid gland. Most T3 is bound to protein in the blood. Free T3 measures the level of T3 that is free, or unbound to protein, and is available to regulate metabolism.
This test looks for antibodies to thyroglobulin, a protein which is specific to the thyroid gland. Under normal circumstances it does not enter the bloodstream, but if your thyroid is inflamed or under attack from the body's own immune system, then thyroglobulin can be secreted and antibodies detected.
Raised levels of thyroglobulin antibodies (TGAb) can indicate autoimmune thyroid disease.
Thyroid peroxidase is an enzyme which is produced in the thyroid gland and is important for converting T4 to the biologically active T3. This test looks for antibodies to thyroid peroxidase (TPOAb) in the blood which indicates that the body's immune system is attacking the thyroid gland and impairing its function.
Raised levels of thyroid peroxidase antibodies are often found in Hashimoto's disease (underactive thyroid) and can sometimes be detected before any symptoms are reported.
Raised levels are also found in over half the cases of Graves' disease (overactive thyroid).