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 T3 and T4 produced, a "message" is sent to the pituitary gland ordering it to increase its TSH secretion, with the aim of stimulating the thyroid. This process is called the positive feedback loop. For this reason, analyzing the TSH blood level provides information on the quantity of thyroid hormones present. High TSH levels are indicative of hypothyroidism
, and further investigation is required to find the cause of the imbalance.