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Thyroid function tests (TFTs) is a collective term for blood tests used to check the function of the thyroid. [1] TFTs may be requested if a patient is thought to suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy.
The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland.
The concentration of thyroid hormones (T 3 and T 4) in the blood regulates the pituitary release of TSH; when T 3 and T 4 concentrations are low, the production of TSH is increased, and, conversely, when T 3 and T 4 concentrations are high, TSH production is decreased. This is an example of a negative feedback loop. [5]
The TSH receptor is a member of the G protein-coupled receptor superfamily of integral membrane proteins [5] and is coupled to the G s protein. [6] It is primarily found on the surface of the thyroid epithelial cells, but also found on adipose tissue and fibroblasts. The latter explains the reason of the myxedema finding during Graves disease.
For example, thyrotropin-releasing hormone (TRH) is released from the hypothalamus in response to low levels of secretion of thyroid-stimulating hormone (TSH) from the pituitary gland. The TSH in turn is under feedback control by the thyroid hormones T4 and T3. When the level of TSH is too high, they feed back on the brain to shut down the ...
Deutsch: Referenzbereiche für die Sekretionsleistung der Schilddrüse (SPINA-GT) und den TSH-Index nach Jostel (TSHI oder JTI) verglichen mit univariablen Referenzbereichen für Thyreotropin (TSH) und freies Thyroxin (FT4), dargestellt im zweidimensionalen Phasenraum, der durch TSH- und FT4-Serumkonzentrationen definiert ist.
Therefore, when TRH is given exogenously, TSH levels increase. If the increase in serum TSH level following TRH administration is absent or very slight, then the cause of the hypothyroidism is in the anterior pituitary gland, i.e. the pituitary is not secreting TSH. Therefore, even when TRH is given exogenously, TSH levels do not rise as the ...
The TSH index is reduced in patients with secondary hypothyroidism resulting from thyrotropic insufficiency. [1] [9] [10] [11] For this indication, it has, however, up to now only been validated in adults. [12] JTI was also found reduced in cases of TACITUS syndrome (non-thyroidal illness syndrome) as an example of type 1 thyroid allostasis.