TSH stands for thyroid stimulating hormone, which is also called thyrotropin. This is an extremely important hormone produced in the pituitary gland that aids in the function of the thyroid gland, and its release of two hormones called triiodothyronine (T3) and thyroxine (T4). T3 and T4 are indicated in controlling normal development of children, including brain development, and a variety of other functions in the body. People who have too much (hyperthyroidism) or too little (hypothyroidism) of these hormones can develop very serious medical problems.
Often if thyroid problems are suspected, doctors will order what is called a TSH test, as one way of evaluating whether enough of this hormone exists to produce adequate levels of T3 and T4. There are many in the medical community who criticize this practice when it is used alone and not with other tests that evaluate actual levels of T3 and T4. A TSH test can be a good place to start to determine if low levels of this hormone exist, however. Tests are a little difficult to read because actual levels can fall into a significant range, and there is some debate on whether the range considered normal is too generalized. Some people who fall within low normal, especially those with bipolar conditions, may benefit from supplementation with T4 and/or T3 to control mood.
Certain conditions are not evident with a TSH test, and these include Hashimoto's thyroiditis. This autoimmune condition treats the hormones produced in the thyroid as foreign and will act to destroy them. One of the tests that can more accurately diagnose this condition is a thyroid antibodies test. People with this condition may have normal TSH levels and thus miss important diagnosis.
When thyroid stimulating hormone levels are considered low, it usually indicates an overactive thyroid, or hyperthyroidism. Doctors may use medications to slow thyroid hormone production, and in some cases, the thyroid gland is removed and people are given thyroid medications instead so that these hormones continue to be available in the body in appropriate and helpful amounts. High TSH levels may suggest hypothyroidism, and this can be just as dangerous as very high thyroid levels. Normal supplementation is with T4, although some people also benefit from supplementing with T3 too.
One of the times that it is most vital to test thyroid stimulating hormone and presence of the hormones it stimulates is in early infancy. Children with high levels of TSH and low levels of T3 and T4 may not have adequate thyroid hormones for normal physical and mental development. In many countries, TSH and other thyroid tests are performed within the first few days of an infant's life to make certain that thyroid levels are well within normal range.