TSH; thyrotropin, thyrotrophin
Thyroid stimulating hormone is produced and released into the bloodstream by the pituitary gland. It controls production of the thyroid hormones, thyroxine and triiodothyronine, by the thyroid gland by binding to receptors located on cells in the thyroid gland. Thyroxine and triiodothyronine are essential to maintaining the body’s metabolic rate, heart and digestive functions, muscle control, brain development and maintenance of bones.
When thyroid stimulating hormone binds to the receptor on the thyroid cells, this causes these cells to produce thyroxine and triiodothyronine and release them into the bloodstream. These hormones have a negative effect on the pituitary gland and stop the production of thyroid stimulating hormone if the levels of thyroxine and triiodothyronine are too high. They also switch off production of a hormone called thyrotropin-releasing hormone. This hormone is produced by the hypothalamus and it also stimulates the pituitary gland to make thyroid stimulating hormone.
A simple blood test can measure thyroid stimulating hormone in the circulation. If a person has too much, this may indicate that their thyroid gland is not making enough thyroid hormone, that is, they have an underactive thyroid gland or hypothyroidism. People with an underactive thyroid often feel lethargic, experience weight gain and feel the cold. Their thyroid gland may enlarge to produce a goitre. Treatment is medication in the form of tablets to bring the level of thyroid hormones back to normal. This also reduces the amount of thyroid stimulating hormone in circulation. It is particularly important for pregnant women to have the correct amounts of thyroid stimulating hormone and thyroid hormones to ensure the healthy development of their babies. Thyroid stimulating hormone is one of the hormones measured in newborns. Rarely, problems from the pitutiary gland or rare genetic conditions can result in inappropriately high thyroid stimulating hormones, and high free thyroid hormone levels.
If a person has too little thyroid stimulating hormone, it is most likely that their thyroid gland is making too much thyroid hormone, that is, they have an overactive thyroid or hyperthyroidism, which is suppressing the thyroid stimulating hormone. People with an overactive thyroid have the opposite symptoms to those with hypothyroidism, i.e. they lose weight (despite increasing the amount they eat), feel too hot and can experience palpitations or anxiety. They may also have a slightly enlarged thyroid gland. Treatment is medication in the form of tablets, which reduce the activity of the thyroid gland and return all thyroid hormone levels to normal. Rarely, problems in the pituitary gland can also result in a low thyroid stimulating hormone, and low free thyroid hormone levels.
Last reviewed: Mar 2018