TSH, or thyroid stimulating hormone, is the hormone released by the pituitary gland, regulating the levels of T3 and T4.
Normal TSH levels indicate that you have a healthy thyroid gland and a balance in the regulatory system controlling the release of thyroid hormones.
Measuring TSH gives you information on the circulating amounts of TSH in your bloodstream. Since the release of TSH is regulated by the pituitary gland in the brain, TSH levels can provide information on the function of this regulatory system, as well as to find out if the thyroid gland is properly functioning.
TSH can also be measured to evaluate and track treatment effectiveness of thyroid gland disorders. If doses have been changed, it is recommended to wait for 6-8 weeks before taking a new TSH test for evaluation.
High levels of TSH can indicate that your thyroid isn’t making enough thyroid hormone, also known as hypothyroidism. Increased TSH levels can either be caused by an isolated increased release from the pituitary gland, or as a result of low circulating levels of T3 and T4 (as a result of a malfunctioning thyroid gland) through a feedback loop signaling the need for increased TSH release.
Common causes of hypothyroidism are inflammation in the thyroid gland (thyroiditis) and treatment therapies such as surgery and radiation therapy.
Important note: TSH alone isn’t enough to investigate the function of the thyroid gland, and needs testing of other thyroid biomarkers such as T4 together with associated symptoms and sometimes even further diagnostic tools.
Low levels of TSH most likely means that your thyroid gland is overactive producing too much thyroid hormone, also known as hyperthyroidism. This is suspected if T4 is simultaneously high.
Common causes of hyperthyroidism include an autoimmune disorder called Grave’s disease, excess intake of iodine and inflammation in the thyroid gland known as thyroiditis.
If T4 is instead also low, one must consider the risk of pituitary gland deficiency.