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The thyroid hormone T4

What is the hormone T4 (thyroxine)?

T4 thyroid hormone is produced by the cells of thyroid follicles. Thyrocytes synthesize from amino acids and iodine to the thyroglobulin, which is a precursor of thyroxine. The thyroglobulin stored in the follicles and if necessary, by separation of the fragments produces thyroxine.

The main action of the T4 hormone is to accelerate catabolism – the process of obtaining energy from the energetically important metabolites (glycogen, fat). The excessive concentration of thyroxine in the blood causes palpitations, irritability, reduction of body weight. But this does not mean that the hormone is harmful, it is only the symptoms of overdose. Normal tetraiodothyronine supports the tone of the nervous system, heart rate and adequate metabolism.

Hormone T4 is not the active thyroid hormone, for comparison, his activity is almost ten times lower than triiodothyronine. The latter is also called the hormone T3, as its formula contains 3 iodine atoms. T3 may be formed in the cells of the gland itself as well as in the cells of the body from its predecessor – thyroxine. In fact, he is the more active metabolite of T4.

Hormones T3, T4 is also referred to as thyroid hormone, as their secretes thyroid, called in Latin "thyroid". TSH is also sometimes referred to thyroid, but this is mistaken, because it is produced by the pituitary gland in the brain, and controls hormonebased gland function.

Often together with the analysis of blood on hormones TTG, T3, T4 are simultaneously determined by antibodies to TPO and thyroglobulin. These figures are usually endocrinologists use to diagnose pathologies of the thyroid gland. Sometimes thyroid hormones examined in the treatment of disease to determine its dynamics and the effectiveness of prescribed therapy. In this article will provide information about what is the T4 hormone which it functions in the body and how is the interpretation of the analysis of its content.

Hormone T4 belongs to the group of iodine-containing thyroid hormones. As part of its chemical formula there are two amino acid residue of tyrosine and four atoms of the halogen iodine. Synonyms of the hormone T4 are tetraiodothyronine, and thyroxin. The name of the substance was due to the number of iodine atoms contained in the molecule. Due to the simple structure of the concentration tetrajodtironina can be easily determined in the laboratory. For the same reason hormonecan be synthesized by artificial means that are used in hormone therapy.

The T4 hormone in the blood

In the bloodstream, the T4 hormone is mostly associated with the protein condition. When the follicles in the thyroid produces thyroxine, it is a special protein thyroxine binding globulin (TSG). This ingredient performs a transport function, delivering the hormone to the body cells. The small number is not associated with protein is called thyroxine T4 free. It is this faction responsible for ensuring biological effect. Part of the hormone which is in connection with TSG, called T4 are connected. If individually to determine blood free T4 and T4 bound, and then we add up these values, we get T4 overall.

In the body the primary effect is the free thyroid hormones (free T4, free T3), so their content is of the highest importance to determine pathologies of the thyroid gland. Laboratories often carried out blood testing for thyrotropin and free T4. The increased TSH is used to assess the regulation of thyroid gland by the pituitary gland, and the free T4 as the main hormone glands directly reflects its function. The concentration of free T4 is increased in hyperthyroidic States or as a result of an overdose of hormonal methods used for therapy of hypothyroidism.

Analysis of the hormone T4

In clinical practice endocrinologists hormone blood TSH, T4 is the most commonly used method of diagnosis. Hormonal studies are assigned in various combinations, based on symptoms and economic empowerment of the patient.

During the initial visit to the endocrinologist, if the patient has no symptoms, is enough to hand over the analysis on hormones TSH, T4, T3. With regard to the latter two hormones, the better to explore their active, i.e. free fraction. In cases where the patient is receiving thyreostatics regarding the treatment of the early stages of graves disease (diffuse toxic goiter), it is better to define only the free hormones T3 and T4. Under the action of tireostaticheskim there is a rapid decrease of these indicators, while the TSH level as if late and no time to decrease.

If a patient is treated for a long time about the lack gland function, for periodically monitoring the quality of therapy is sufficient to determine only the concentration of thyroid stimulating hormone (TSH). Free T4 is examined only when there are specific indications. Should knowthat in the case of reception of a thyroxine, a blood test for the hormone T4 can be taken only prior to his admission. Failure to comply with this rule, the result of the analysis will be uninformative as to the hormone T4 that is allocated by the thyroid gland, added to the amount of thyroxine that went along with the accepted drug.

In pregnancy, the value of the free T4 hormone is particularly improved, because the level of thyrotropin may be reduced as a result of HCG - human chorionic gonadotropin produced by the placenta. Therefore, when pregnant women definition just TSH is not sufficient for a correct diagnosis. You need to be tested simultaneously on TSH and T4.

In the direction or form with the result of the study can be found in various cuts:

  • FT4, FT3 – T4 and T3 free (eng. free means "free");
  • Hormone FT4, T3 SV hormone – free forms of the hormones.

What is the rate of T4 hormone?

Hormone-free T4. In order to assess the results of the analysis on hormone-free T4, not enough to know any specific rules. The normal concentration of thyroxine is largely dependent on the laboratory conducting the analysis. For different analyzers these indicators are different, the value is even used in each case, the set of reagents. As a rule, the maximum concentration of T4 in the blood specified on the form after the result of the analysis. When using high-quality laboratory equipment of 3 generation in healthy people, the concentration of thyroxine is in the range of about 9 - 20 pmol/L.

Total hormone T4. Indicators such as total hormone T4 depends on the physiological state of the organism. For example, in pregnant women it increases. Therefore, the normal range for total thyroxine more variable than that of its free fraction.

The hormone T4 (tetraiodothyronine) shared

The age of the patient




59 — 135

4.6 — 10.5


71 — 142

5.5 — 11


75 — 230

5.8 — 17.9

Children: 1-5 years

90 — 194

7 — 15

Children: 5-10 years

83 — 172

6.5 — 13.4

T4hormone (tetraiodothyronine) free

The age of the patient




9.0 — 22.0

0.7 — 1.71


7.6 — 18.6

0.6 — 1.45

Children: 5-10 years

10.7 — 22.2

0.83 — 1.73

Children: 10-15 years

12.1 — 26.9

0.94 — 2.09

! Important: As in the analysis of hormones it is possible to recognize the disease thyroid?

Hormone T4 is elevated

For excessive levels of the hormone T4, characterized by the following symptoms:

Increased hormone T4 speeds up the breakdown of fat in the body and reduced body mass. An excessive amount of the released energy has a negative impact on organ function. This is manifested in the acceleration and strengthening of the heart, increased sweating. Excessive stimulation of the nervous system causes irritability and frequent mood swings, and acceleration of neuromuscular transmission leads to tremor of the limbs. Weight loss while this condition is not physiological, because it occurs on the background of violations of functions of internal organs. With long-term preservation of high concentrations of thyroxine from the bones leaches calcium, resulting in increased risk of fractures and osteoporosis.

The reasons for the increase of the hormone T4 (total and free):

Hormone T4 lowered

Low T4 hormone normally associated with insufficient hormonal function of thyroid gland. This condition is called hypothyroidism.

The reasons for the low level of the hormone T4 are the following States:

  • Treatment of hyperthyroidism with thyreostatics or radioactive iodine;
  • Autoimmune thyroiditis (the body produces antibodies against the cells of the thyroid follicles, which leads to insufficient production of thyroxine);
  • The removal of the prostate gland or parts of it surgically.

There are times when seemingly healthy people hormone-free T4 is lowered. Most often this is due to errors when doing research in the lab. When you recheck in a more high quality laboratory centers is that the concentration of thyroxine normal. To avoid errors in diagnosis, it is necessary to consider the clinical picture and the value of the TSH level. In all cases, when the analysis of low T4 hormone, and the hormone TSH is in the normal range, you should be cautious to interpret the result and to repeat the study.

If you re in a good laboratory again showed reduced levels of thyroxine, it is necessary to refer to the endocrinologist. Failure of function of thyroid gland, as a rule, is lifelong in nature. Therefore, it is necessary to conduct continuous therapy with the appointment of the synthetic hormone T4. These artificially thyroxine are identical in structure to the natural hormone, and when properly selected dose does not cause any side effects.

Causes of low hormone T4 (total and free):

  • Sheehan's Syndrome;
  • Congenital and acquired goiter;

  • Autoimmune thyroiditis;

  • Traumatic brain injury;
  • Inflammatory processes in the pituitary gland and hypothalamus;
  • Hypothyroidism

  • Treatment with tamoxifen, antithyroid drugs (merkazolil, PTU), steroids, anabolics, beta-blockers (metoprolol, propranolol), NSAIDs (diclofenac, ibuprofen), statins (atorvastatin, simvastatin), anti-TB and anticonvulsant medications, diuretics, lithium salts, reception rentgencontrastnykh substances.

Hormone T4 in pregnancy

The level of thyroxine plays a very important role in the development of the fetus. Hormone-free T4 in the first 3 months of pregnancy provides the development and growth of the nervous system of the embryo, therefore, its deficiency may lead to various congenital abnormalities. The content of thyroxine in women and men is approximately the same, but during pregnancy it is not recommended to determine the level of total T4. A pregnant women is a physiological increase in synthesis of thyroxine binding globulin, and it binds a large part of T4 in the blood stream. Definition during this period, total T4 uninformative, so its value will always be high, despite the fact that the free fraction of the hormone is normal.

During pregnancy you need to take the hormone-free T4, this will help to objectively evaluate the work of the gland. It happens that in healthy pregnant women there is a slight increase in free thyroxine, not requiring treatment. But if this figure is considerably higher than the upper limit, it is necessary to reduce the rate through medication. The treatment is carried out very carefully, under the constant control of thyroxine, to ensure the normal development of the fetus.