TSH, also known as thyroid stimulating hormone, is a peptide hormone secreted by the pituitary gland, which promotes the synthesis and secretion of thyroid hormones and regulates the functional state of the thyroid gland through the hypothalamic-pituitary-thyroid axis. the causes of high TSH are as follows. I. Pituitary lesions, when pituitary tumors or a history of pituitary hyperplasia can appear elevated thyrotropic hormone, elevated thyrotropic hormone stimulates the secretion of thyroid hormone, which can lead to pituitary hyperthyroidism. Second, hypothyroidism, when the thyroid gland secretes less T3 and T4, the inhibitory effect on thyroid stimulating hormone is weakened and high thyroid stimulating hormone occurs. Hypothyroidism occurs when there is both elevated thyroid stimulating hormone and decreased T3 and T4. When only thyroid stimulating hormone is elevated, but T3 and T4 are normal, the condition is considered subclinical hypothyroidism.