tsh is thyroid-stimulating hormone produced by the pituitary gland in the brain. tsh stimulates the thyroid gland to produce and release thyroid hormone into the blood. thyroid hormone maintains normal metabolism growth body temperature and many other essential bodily functions. blood levels of tsh and thyroid hormone are maintained in a tight balance. high levels of thyroid hormone cause the pituitary to reduce the release of tsh. low levels of tsh lead the pituitary to release more tsh. this in turn stimulates the thyroid gland which produces more thyroid hormone which reduces the tsh level. this relationship is called a negative feedback loop. doctors use the blood tsh level as a screening blood test for thyroid function: high tsh usually means an underactive thyroid (hypothyroidism). low tsh is usually due to an overactive thyroid (hyperthyroidism). in people being treated for hypothyroidism or hyperthyroidism tsh also provides information on the success of treatment.
what is tsh?