Clinical Significance

Human thyroid-stimulating hormone is a glycoprotein hormone consisting of two noncovalently-bound subunits: an alpha subunit, which is nearly identical to the alpha subunits of human luteinizing hormone (hLH), human follicle-stimulating hormone (hFSH), and human chorionic gonadotropin (hCG) and a beta subunit, which is responsible for immunlogical and biological speceficity.

TSH, released from the anterior pituitary, is the principal regulator of thyroid function, stimulating the synthesis and release of thyroid hormones thyroxine (T4) and triiodothyronine (T3). T3 and T4 regulate biochemical processes that are essential for normal metabolism. The synthesis and secretion of TSH is stimulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus in response to low levels of circulating T3 and T4. In contrast, elevated levels of T3 and T4 suppress the production of TSH. Collectively, this negative feedback system is referred to as the hypothalamic-thyroid axis. Any alteration in the function of this axis can influence the levels of TSH, T4, and T3 in circulation.

The principal clinical use for TSH measurement is for the assessment of thyroid status. TSH is measured in conjunction with thyroid hormones or antibodies to: 1) detect or exclude hypothyroidism or hyperthyroidism; 2) monitor T4 replacement treatment in hypothyroidism or antithyroid treatment in hyperthyroidism; 3) monitor TSH suppression in thyroid cancer patients on thyroxine therapy; and 4) assess the response to TRH stimulation testing.

_{Source: Access TSH3 IFU #B83033G, 06-2017}