Low TSH level - Definition

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Definition


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 large quantities of T3 and T4 produced, a "message" is sent to the pituitary gland ordering it to reduce its TSH secretion, with the aim of stopping the thyroid stimulation. This process is called the negative feedback loop. For this reason, analyzing the TSH blood level provides information on the quantity of thyroid hormones present. When the TSH level drops it is indicative of hyperthyroidism, and further investigation is required to find the cause of the imbalance.