TSH (also referred to as thyroid stimulating hormone, thyrotropic hormone or thyrotropin) is a hormone produced by the pituitary, a gland located inside the skull.
TSH stimulates the thyroid to produce thyroid hormones predominantly thyroxine (T4) but also small amounts of triiodiothyronine (T3).
Thyroid hormones, in turn, are able to regulate the production of TSH by the pituitary gland. In fact, under normal conditions, if the concentration of thyroid hormones in the blood tends to decrease, the pituitary gland increases the production of TSH. The thyroid gland responds to the increase in TSH in the blood by producing more thyroid hormones to restore balance. When the levels of thyroid hormones in the blood become normal, the pituitary gland reduces the production of TSH.
The cycle repeats itself continuously with the aim of maintaining constant levels of thyroid hormones in the blood (Video).
In conditions of malfunctioning of the thyroid, this balance is disrupted. In fact, if the levels of thyroid hormones are too high (hyperthyroidism) the pituitary does not produce TSH and the levels of the TSH hormone in the blood become so low that they cannot be measured.
Otherwise, if the thyroid is not functioning sufficiently, thyroid hormone levels become too low (hypothyroidism) and the pituitary gland increases TSH production in an attempt to stimulate the thyroid to produce more hormones.
The TSH test consists of measuring the amount of TSH in the blood and is used for:
- carry out birth checks (newborn screening) to ascertain as soon as possible the possible presence of congenital hypothyroidism
- discover thyroid disease and follow in time (to monitor) the effectiveness of the treatments in people with hypothyroidism or hyperthyroidism
- to investigate problems of infertility in women
- evaluate the function of the pituitary gland
The TSH test is done by simply drawing blood from a vein in the arm. It is not necessary to be fasting, but if you are taking the replacement hormone (levothyroxine) it must be taken before taking it.
The TSH test is also performed as a control test to check the presence of congenital hypothyroidism in all newborns (law 104 of 5/2/1992 and DPCM of 9/7/1999). In this case, the blood is taken from the heel: a few drops are enough to place on a special card.Results
The TSH test results must be compared with the reference values provided by the analysis laboratory, bearing in mind that these values may also vary according to age.
Generally speaking, it can be said that an elevated TSH value is often linked to an underactive thyroid gland, that is to say that it produces an insufficient quantity of thyroid hormones (hypothyroidism); or in people being treated for hypothyroidism it is an indication of an "insufficient intake of replacement hormone.
Very rarely, a high TSH value can indicate a problem in the pituitary gland that results in loss of control of the hormone production and regulation systems, for example, a tumor.
Conversely, a low TSH value may indicate an overactive thyroid (hyperthyroidism). However, low TSH can also be seen in people with hypothyroidism who take too much replacement hormone.
Rarely, a low TSH can be a sign of damage to the pituitary gland that prevents hormone production.
It is important to underline that an altered TSH value indicates an excess or a defect of thyroid hormones in the blood, but does not highlight the cause. For this reason, a TSH test with an altered result is usually followed by the execution of further tests necessary to understand the causes that led to this result.
It is good to remember that whatever the test result is, it must always be viewed and interpreted by your doctor.Bibliography
Law 5 February 1992, n. 104. Framework law for assistance, social integration and the rights of handicapped persons (Official Gazette. General series no. 39 of 02.17.1992)
Decree of the President of the Council of Ministers 9 July 1999. Act of guidance and coordination for the regions and autonomous provinces of Trento and Bolzano on the subject of checks useful for the early diagnosis of malformations and mandatory "control for the" identification and timely treatment of congenital hypothyroidism, phenylketonuria and cystic fibrosis (Official Gazette. General Series n.170 of 07/22/1999)