Total thyroxin in serum

T4 - the main hormone of the thyroid gland. Its concentration in the blood exceeds that of T3 by 60 times. The elimination half-life is 5-7 days. The reference concentration values ​​of total T4 in blood serum are presented in the table.

Table Reference values ​​for total T4 concentration in blood serum

Table Reference values ​​for total T4 concentration in serum

In the majority of patients with clinically expressed hyperthyroidism, the T4 content in the blood is increased,hypothyroidism is reduced. However, in some cases, the concentration of T4 in the blood does not reflect the functional state of the thyroid gland. These include the conditions under which the concentration of TSH changes. For example, the concentration of T4 in the blood can be increased with increasing TSH.The latter can be due to a genetically determined increase in the content of TSH, as well as pregnancy, the intake of contraceptives containing derivatives of es-tragiol, estrogen therapy. At the same time, the concentration of T4 in the blood can be reduced by decreasing the binding ability of TSH.This is caused by the following pathological conditions: chronic hepatic diseases, nephrotic syndrome, genetically

deterministic reduction of TSG synthesis. Androgen therapy also reduces the binding ability of TSH.In old age, in 20% of people with euthyroid status, the concentration in blood of TSH decreases, which, in turn, leads to a decrease in the T4 level.

Temporarily increase the concentration of total T4( pseudodysfunction of the thyroid gland) observed in almost 20% of patients entering psychiatric clinics. Concentration of total T4 may also increase in other diseases not associated with changes in thyroid function. In such patients, T4 usually normalizes after a few days without treatment. In favor of pseudodysfunction of the thyroid gland is indicated by a reduced concentration of total T3 and normal TSH content.

An increase in the concentrations of total T4( and total T3) without the effects of thyrotoxicosis is possible with a rare hereditary disease - generalized resistance to thyroid hormones. Despite an increase in the concentrations of T4, cT4, T3 and free triiodothyronine( cT3), patients have an euthyroid condition, and in some even mild hypothyroidism.

The main diseases and conditions at which the serum T4 concentration is changing are shown in the table.

Table Diseases and conditions at which the serum T4 concentration of