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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.
Free T4, total T3 or both are elevated and serum TSH is below normal in hyperthyroidism. If the hyperthyroidism is mild, only serum T3 may be elevated and serum TSH can be low or may not be detected in the blood. [14] Free T4 levels may also be tested in patients who have convincing symptoms of hyper- and hypothyroidism, despite a normal TSH.
The initial endocrine evaluation includes testing for levels of TSH and free T4, prolactin, LH, FSH, estradiol (E2), and anti-Müllerian hormone (AMH). [9] FHA patients may display a combination of the following: FSH concentrations that are normal but lower than LH levels, low or low normal LH, E2 <50 pg/mL, and progesterone <1 ng/mL. [6]
T 3 is preferred, because in hypothyroidism T 3 levels may be normal. [84] The ratio of bound to unbound thyroid hormones is known as the thyroid hormone binding ratio (THBR). [ 85 ] It is also possible to measure directly the main carriers of the thyroid hormones, thyroglobulin and throxine-binding globulin. [ 86 ]
For most substances presented, the optimal levels are the ones normally found in the population as well. More specifically, optimal levels are generally close to a central tendency of the values found in the population. However, usual and optimal levels may differ substantially, most notably among vitamins and blood lipids, so these tables give ...
The standard definition of a reference range for a particular measurement is defined as the interval between which 95% of values of a reference population fall into, in such a way that 2.5% of the time a value will be less than the lower limit of this interval, and 2.5% of the time it will be larger than the upper limit of this interval, whatever the distribution of these values.
The target level for TSH is the subject of debate, with factors like age, sex, individual needs and special circumstances such as pregnancy being considered. [79] Recent studies suggest that adjusting therapy based on thyroid hormone levels (T 4 and/or T 3 ) may be important.
Normal thyroid levels are also seen, and occasionally also hypothyroidism, which may assist in causing goiter (though it is not the cause of the Graves' disease). Hyperthyroidism in Graves' disease is confirmed, as with any other cause of hyperthyroidism, by measuring elevated blood levels of free (unbound) T3 and T4.