Description

• If the thyroid gland fails the concentrations of T4 and T3 fall resulting in increased TSH release from the pituitary gland.
• If the thyroid gland becomes overactive and increased amounts of thyroid hormones are released, TSH production will be suppressed.
• In a variety of illnesses not directly affecting the thyroid, the mechanism of TSH release may not function properly, so the release of TSH may be reduced and blood T4 and T3 may fall as a result. In this situation, because the pituitary does not respond, TSH is not elevated.
• In some cases of pituitary failure TSH production does not occur normally (often associated with decreased or increased production of other hormones). Very rarely, TSH concentrations may be increased, due to a tumour of the pituitary, in which case the thyroid will make and release increased amounts of T4 and T3, and the patient may experience symptoms associated with hyperthyroidism