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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.
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 ...
The most useful marker of thyroid gland function is serum thyroid-stimulating hormone (TSH) levels. 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 ...
If the TSH level is normal or low and serum free T 4 levels are low, this is suggestive of central hypothyroidism (not enough TSH or TRH secretion by the pituitary gland or hypothalamus). There may be other features of hypopituitarism , such as menstrual cycle abnormalities and adrenal insufficiency .
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 ...
They may reveal hyperthyroidism (high T 3 and T 4), hypothyroidism (low T 3, T 4), or subclinical hyperthyroidism (normal T 3 and T 4 with a low TSH). [84] TSH levels are considered the most sensitive marker of thyroid dysfunction. [84] They are however not always accurate, particularly if the cause of hypothyroidism is thought to be related to ...