TSH stands for Thyroid Stimulating Hormone. A high TSH result often means an under-active thyroid gland (hypothyroidism) that is not responding adequately to the stimulation of TSH due to some type of acute or chronic thyroid dysfunction. Rarely, a high TSH result can indicate a problem with the pituitary gland, such as a tumor producing unregulated levels of TSH, in what is known as secondary hyperthyroidism. A high TSH value can also occur when patients with a known thyroid disorder (or those who have had their thyroid gland removed) are receiving too little thyroid hormone medication. A low TSH result can indicate an overactive thyroid gland (hyperthyroidism) or excessive amounts of thyroid hormone medication in those who are being treated for an underactive (or removed) thyroid gland. Rarely, a low TSH result may indicate damage to the pituitary gland that prevents it from producing adequate amounts of TSH.