Plain explanations of the terms used across this site. Where a term appears in bold elsewhere on the site, it is defined here.
Antibodies (TPO, Tg, TRAb). Proteins made by the immune system. In thyroid disease, raised TPO or Tg antibodies suggest Hashimoto’s, while TRAb is linked to Graves’ disease.
Autoimmune. A condition in which the immune system mistakenly attacks the body’s own tissue, as in Hashimoto’s and Graves’ disease.
Carbimazole. An antithyroid medicine that reduces how much hormone an overactive thyroid produces.
Central hypothyroidism. An underactive thyroid caused by a problem in the pituitary or hypothalamus rather than the gland itself.
Cortisol. The main stress hormone, made by the adrenal glands. High long term cortisol can disturb thyroid function.
Deiodinase. An enzyme that converts the storage hormone T4 into the active hormone T3.
DTE or NDT. Desiccated thyroid extract, also called natural desiccated thyroid, made from animal thyroid and containing both T4 and T3.
Free T3 (FT3). The small, unbound fraction of T3 in the blood that is available for cells to use.
Free T4 (FT4). The small, unbound fraction of T4 in the blood that is available to be converted into T3.
Goitre. A visible swelling of the thyroid gland at the front of the neck.
Graves’ disease. An autoimmune cause of an overactive thyroid.
Hashimoto’s thyroiditis. An autoimmune cause of an underactive thyroid, and the most common cause of hypothyroidism.
HPA axis. The hypothalamic pituitary adrenal axis, the body’s stress hormone control system.
HPT axis. The hypothalamic pituitary thyroid axis, the feedback loop that controls thyroid hormone levels.
Hyperthyroidism. An overactive thyroid, producing too much hormone.
Hypothyroidism. An underactive thyroid, producing too little hormone.
Levothyroxine. A synthetic copy of T4 and the standard treatment for an underactive thyroid.
Liothyronine. A synthetic copy of the active hormone T3.
Reverse T3. An inactive form produced from T4, which can rise during stress or illness.
Subclinical. A stage where TSH has shifted but thyroid hormone levels are still within range; symptoms may still be present.
Thyroidectomy. Surgery to remove part or all of the thyroid gland.
TSH. Thyroid stimulating hormone, released by the pituitary to tell the thyroid to make hormone.
TRH. Thyrotropin releasing hormone, released by the hypothalamus to stimulate the pituitary.
T3. Triiodothyronine, the active thyroid hormone.
T4. Thyroxine, the storage or precursor thyroid hormone.