The endocrine system consists of many different hormone-secreting organs. One hormone in the endocrine system, called thyroid stimulating hormone, works to control the production of hormones in the thyroid. Abnormal thyroid stimulating hormone levels can be caused by pituitary or thyroid dysfunction and can be treated in different ways depending on the thyroid's health.
Function
Thyroid stimulating hormone is made by the pituitary gland. This hormone, which is also known as TSH, stimulates the thyroid gland to make more of its hormones, which are also known as T3 and T4. The thyroid hormones have a negative feedback effect on the production of thyroid stimulating hormone, which means that TSH is typically not made when there are large quantities of T3 and T4 in the blood.
TSH Measurement
TSH is typically measured via a blood test. A blood sample can be taken from the patient's arm veins or, in the case of an infant, from the back of the child's heel. The amount of TSH is then measured using chemicals that react with this hormone. The normal values of TSH are between 0.4 and 4 mIU per liter. The unit mIU is a standard unit for laboratory tests that measure hormone concentrations in the body.
Causes of High TSH
Because TSH is controlled in part by the levels of T3 and T4 in the blood, elevated levels of TSH can be caused by problems with the thyroid gland. If the thyroid gland is malfunctioning, it can cause a condition known as hypothyroidism. The pituitary gland will attempt to stimulate the thyroid gland by producing large amounts of TSH. In some rare cases, a TSH-producing tumor will develop in the pituitary, which can also lead to elevated TSH levels.
Causes of Low TSH
Low levels of TSH can also be caused by problems with the thyroid itself. As the National Institute of Diabetes and Digestive and Kidney Disorders explains, an overactive thyroid gland, also known as hyperthyroidism, will turn off TSH production by the pituitary gland. This result can also occur in patients taking too much thyroid medication, leading to suppression of TSH production. In rare cases, Lab Tests Online indicates, pituitary dysfunction can also lead to low TSH levels.
Treatment
Because the main biological function of TSH is to control T3 and T4 production by the thyroid, most treatments for abnormal levels of TSH focus on ensuring that the proper amount of T3 and T4 are present in the body. Patients with hypothyroidism often need to take synthetic thyroid hormone to keep their levels in the normal range. Patients with an overactive thyroid can attempt to have the underlying defect treated or can simply have their thyroid removed, at which point they will need to take synthetic thyroid hormone daily. Many patients only take synthetic T4 because it can be converted by the body into T3 as needed, though some doctors will prescribe a regimen of both T4 and T3.
