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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.
Any inappropriateness of measured values, for instance a low-normal TSH together with a low-normal T 4 may signal tertiary (central) disease and a TSH to TRH pathology. Elevated reverse T 3 (RT 3) together with low-normal TSH and low-normal T 3, T 4 values, which is regarded as indicative for euthyroid sick syndrome, may also have to be ...
It is also beneficial for assessing the severity of already confirmed thyroid hormone resistance, [6] even on replacement therapy with L-T4, [7] and for monitoring the pituitary response to substitution therapy with thyromimetics (e.g. TRIAC) in RTH Beta. [8] In autoimmune thyroiditis the TTSI is moderately elevated. [9]
Affected patients may have normal, low, or slightly elevated TSH depending on the spectrum and phase of illness. Total T4 and T3 levels may be altered by binding protein abnormalities, and medications. Reverse T3 levels are generally increased, while FT3 is decreased. FT4 levels may have a transient increase, before becoming subnormal during ...
TSH levels are determined by a classic negative feedback system in which high levels of T3 and T4 suppress the production of TSH, and low levels of T3 and T4 increase the production of TSH. TSH levels are thus often used by doctors as a screening test, where the first approach is to determine whether TSH is elevated, suppressed, or normal. [25 ...
The pituitary gland secretes thyrotropin (TSH; Thyroid Stimulating Hormone) that stimulates the thyroid to secrete thyroxine (T4) and, to a lesser degree, triiodothyronine (T3). The major portion of T3, however, is produced in peripheral organs, e.g. liver , adipose tissue , glia and skeletal muscle by deiodination from circulating T4.
Subclinical hypothyroidism is a biochemical diagnosis characterized by an elevated serum TSH level, but with a normal serum free thyroxine level. [47] [48] [49] The incidence of subclinical hypothyroidism is estimated to be 3-15% and a higher incidence is seen in elderly people, females and those with lower iodine levels. [47]
Hypothalamus secretes a hormone called thyrotropin releasing hormone (TRH) which in turn release thyroid stimulating hormone (TSH). TSH signals thyroid to secrete thyroid hormones thyroxine (T4) and triiodothyronine (T3). T4 gets converted to active T3 in peripheral tissues with the help of deiodinase enzymes.
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