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Blood take service 4.00€

LT4 (FT4) | Free thyroxine

LT4 (FT4) | Free thyroxine


Reference: 15124

Determination of free thyroxine (FT4/LT4) is one of the most important tests for thyroid pathology. This hormone, the unbound and biologically active form of thyroxine, is a useful daily clinical diagnostic tool for the assessment of thyroid status. FT4/LT4 is usually determined together with TSH/TTH. The level of free thyroxine (FT4/LT4) in the blood is usually inversely correlated with the level of TSH/TTH. As one of these parameters increases, the other must decrease, and vice versa. If a decrease in TSH/TTH is detected without an increase in FT4/LT4, in this case it is necessary to determine FT3/LT3. FT4/LT4 measurement, unlike TSH/TTH measurement, directly tests thyroid function.

FT4 is increased in hyperthyroidism, Grave's disease, initial stage of subacute thyroiditis. Decreased in hypothyroidism.

Immunological quantitative in vitro assay

Tested in blood serum and plasma. Blood is taken from a vein.


  • It is recommended to carry out prophylactically once a year. Treatment control is carried out periodically according to the doctor's instructions.
  • The accuracy of the test response is affected by the drugs used, an increase is found in hyperthyroidism, a decrease in hypothyroidism, pregnancy.
  • To take the test, you need to arrive without food at 8 o'clock.
LT4 (FT4) | Free thyroxine
LT4 (FT4) | Free thyroxine
Reference: 15124