The thyroid is an endocrine gland which regulates numerous essential physiological processes in many systems of the body, through the production and release of the hormones triiodothyronine (T3) and thyroxine (T4). The thyroid also produces calcitonin, which plays an important role in calcium homeostasis.

Production of T3 and T4 is controlled by several regulatory feedback loops, including thyroid-stimulating hormone (TSH) produced by the pituitary gland, which is itself regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus.

Thyroid diseases may lead to an overproduction (hyperthyroidism, e.g. Grave’s disease) or an underproduction of T3 and T4 (hypothyroidism, e.g. Hashimoto’s thyroiditis).

Given the pivotal role of T3 and T4 in driving many vital processes in the body, thyroid disorders require a thorough diagnostic workup in which laboratory tests play an important role, including but not limited to measuring the following: T3, T4, TSH, TSH receptor antibodies, thyroperoxidase antibodies, thyroglobulin, anti-thyroglobulin antibodies, thyroxine-binding globulin, and calcitonin.