Ultrasensitive TSH - Definition

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TSH, or thyroid stimulating hormone, is a hormone secreted by the pituitary gland and causes the thyroid to increase synthesis of thyroid hormones (T3 and T4). While TSH stimulates the production of thyroid hormones, these hormones themselves have an effect on TSH production. When there are too low quantities of thyroid hormones, they stimulate TSH secretion to, in turn, stimulate their own production. When there are excessive quantities of these hormones, they inhibit TSH secretion in order to stop thyroid stimulation. In thyroid tests, "ultrasensitive TSH" corresponds to the TSH concentration in the blood.