TSH stands for thyroid stimulating hormone, though it is sometimes called thyrotropin or thyrotropic hormone. TSH stimulates the thyroid gland to produce thyroid hormone, which is is critical for the proper function of virtually every cell in the body. TSH is released by the pituitary gland after the gland has been stimulated by thyroid releasing hormone (TRH), which is secreted by the hypothalamus. Thyroid hormone provides negative feedback on the hypothalamus and/or the pituitary to reduce thyroid hormone production and release. TSH measurements are important for diagnosing hypothyroidism and hyperthyroidism. TSH may be measured in conjunction with total thyroxine (T4), total triiodothyronine (T3), free T4, free T3, and reverse T3 concentrations in the serum.
Normal Ranges for TSH:
0.5 - 4.5 mIU/L
0.50 - 4.50 IU/L
High TSH levels are usually caused by primary hypothyroidism or subclinical hypothyroidism. When thyroid levels are low, the hypothalamus and pituitary gland try to increase thyroid hormone production by raising TSH levels. Hypothyroidism may cause weakness and fatigue, cold intolerance, shortness of breath, weight gain, constipation, cognitive problems, dry skin, hoarseness, and swelling (edema).
Some specific causes of high TSH are:
High TSH levels are usually caused by primary hyperthyroidism or subclinical hyperthyroidism. When thyroid levels are high, the hypothalamus and pituitary gland try to decrease thyroid hormone production by lowering TSH levels. Graves' disease is the most common cause of hyperthyroidism, though the other major autoimmune thyroid disease, Hashimoto thyrotoxicosis (i.e. Hashitoxicosis), is also quite common. Hyperthyroidism may cause excessive appetite, anxiety, heart palpitations, sweating, shortness of breath, weight loss, and intolerance to heat.
Some specific causes of low TSH are:
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