T4 (free): normal. Hormone T4 (free): a blood test for thyroid hormones. T4 general: what kind of hormone, its normal indicators and deviations from the norm

When a doctor sends a patient to donate hormones and the value “ ” appears among the results, it becomes curious what kind of hormone it is and what it is responsible for inside the body. What functions does the hormone perform, how is it determined in the blood, what does it affect and what can cause its deficiency? Let's figure it out.

Substance T4 is a free hormone in the body

The T4 hormone in its free form has a very simple structure, which allows it to be easily determined both in the patient's blood and synthesized artificially to compensate for its deficiency in the blood. It is located in the group of iodothyronines, which in turn is built from four atoms of the well-known iodine and two amino acids. Independently in the human body, it is produced by the thyroid gland and takes an active part in the important mission of protein synthesis.

Important! This hormone is of particular importance for women, as it controls the normal functioning of the entire female reproductive system.

It is thanks to him that the process of the appearance of the egg, and then its ovulation, occurs. In addition, it is responsible for changes in body weight and clears blood vessels from cholesterol. Thanks to its work, the central nervous system functions normally, calcium and vitamin A are well absorbed.

The main action of this hormone is to maintain the normal functioning of many functions of the body, it releases energy from fats or glycogens in the body. Free T4 is increased if the woman began to lose weight sharply, she was nervously excitable, sweating appeared, her pulse quickened and there was a feeling of ringing in the ears.

normal hormone levels

Men boast higher values ​​of this indicator, but in both men and women, this hormone gradually fades after 30 years. In women, the free T4 parameter depends on many different factors. It rises in the morning hours from 8 am to 12 am and reaches its peak during these hours. After 23:00 every day and before 4:00 am, its values ​​are minimal. In addition to hours, T4 production is influenced by climate and seasons. From mid-autumn to early spring, the production of this hormone is maximum, and in summer it is produced in minimal quantities. In pregnant women, this hormone is always slightly elevated, as it is involved in the formation of the bones of the unborn child. Normal indicators for each group of people are special:

• Pregnant women of the first trimester 12 - 20 pmol / l;
• Pregnant women of the second trimester 9.5 - 17 pmol / l;
• Pregnant women of the third trimester 8.5 - 15.6 pmol / l;
• Women from 18 to 50 years old 0.9 - 11.8 pmol / l;
• From 50 to 61 years - 0.7 - 5.4 pmol / l
• From 61 to 71 - 0.4 - 3.5 pmol / l;
• Over 70 years old 0.4 - 2.4 pmol / l;
• Men from 18 years old - 10 - 23 pmol / l;
• Children from 0 to 6 months - 16 - 29 pmol / l;
• Children from 6 to 12 months - 15 - 23 pmol / l;
• Children from 1 to 5 years old - 13 -23 pmol / l;
• Children from 5 to 10 years old - 12.7 - 22.2 pmol / l;
• Children from 10 to 17 years old - 12.1 - 22.0 pmol / l.

Minor fluctuations and deviations from normal values ​​are allowed, especially during pregnancy in women, the concentration of t4 may be exceeded.

If you are not satisfied with an unreasonable result, you can retake it in a few weeks, but you should not change the laboratory at the same time. This is due to the fact that in different laboratories they work according to different methods - the patient needs his analyzes to be compared in the dynamics of human development, but if the laboratories are different, then this is not always possible.

Too much hormone in the blood

Attention! It is categorically impossible to additionally take this hormone for weight loss, as this can adversely affect the entire body as a whole and the further functioning of the thyroid gland in particular.

An increase in the level of T4 in the blood causes an increased breakdown of energy and the release of this energy. As a result, the fat deposits of the body melt, and the allocated doses of energy are sent through the body to enhance the normal reactions of the body to hypertrophied reactions. Exceeding the required norm of the hormone T4 greatly affects human health. Symptoms are often pronounced:

• The person is thrown into a cold sweat, although he sweats as if he were hot;
• Irritability, which is not justified by anything, it cannot be controlled even by the patient himself;
• Any little physical or mental labor quickly tires the patient;
• high heart rate;
• Hand tremor;
• Sudden weight loss against the background of an unchanging diet;
• Sometimes it seems that nothing beats in the chest anymore.

Insufficient hormone levels

Insufficient functioning of the thyroid gland and the production of hormones required for work also affects the patient's health. The thyroid gland removed from the patient or its inflammation detected affects the insufficient production of the necessary hormones. And this, in turn, results in negative states of the whole organism. Symptoms include:

• Sudden and unreasonable weight gain;
• Unpleasant feeling of dryness of the skin;
• A sharp deterioration in the cold;
• Violation of the cycle of menstruation;
• The appearance of causeless edema in the morning and after a working day;
• Hair begins to crumble and no drugs have an effect.

In young children, too low can affect developmental delay, both mental and psychophysical. The reason for the lack of free T4 hormone can be an overdose of drugs that are used to treat excessive thyroid function. Also, such severe conditions in which it is not produced in sufficient quantities are detected as a result of taking radioactive iodine or contact with lead and its derivatives.

Attention! Adhering to an overly rigid diet, which is almost completely lacking in protein and iodine, and dependence on heroin-type narcotic drugs can cause hypothyroidism.

This state of the body is dangerous to health, so it is important to control the amount of protein and iodine-containing drugs consumed.

How to take a hormone test

To determine the level of this hormone in the blood, blood from a vein is used. In order for the result to be as true and correct as possible, it is worth refraining from sexual intercourse and drinking alcohol 3-5 days before donating blood. Also, do not lean on sports activities, try to avoid mental and psychological overload. An hour before blood donation, you can not smoke and have breakfast on the day of the test.

After the last meal, at least 8-10 hours should pass, and it is not advisable to take fried or spicy foods at this meal. Within three days before the test, you should stop taking drugs containing iodine, and try not to worry on the day of the test.

Synonyms: Free thyroxine (T4 free, Free Thyroxine, FT4)

An examination of the thyroid gland begins with a study of the hormonal status, in particular, an analysis of the level of thyroxine (T4). Since this hormone performs many diverse and important functions in the body, the laboratory data obtained during the study make it possible to assess the state and performance of the thyroid gland separately and the endocrine system as a whole.

Of all endocrine hormones, T4 accounts for about 90%. After production by the follicular cells of the thyroid gland, thyroxine is released into the blood, where it is bound by globulin proteins. Only 0.1-0.4% of the T4 hormone remains in a free (unbound) form, which determines their high biological activity.

Functions T4 free

• Ensuring cellular metabolism (thermal, energy, protein, vitamin, etc.);
• Stabilization and regulation of physiological processes in the central nervous system;
• Stimulation of the secretion of retinol (vitamin A) in the liver cells;
• Deactivation of triglycerides and "bad" cholesterol in the blood;
• Increased metabolism and bone resorption;
• Strengthening the process of removing calcium from the body (through the urinary system), etc.

The concentration of the hormone T4 in the blood serum changes during the day and reaches its maximum by 8.00 -12.00. The lowest rates are observed late at night. Also fluctuations of a thyroxine depend on a season of year. Experts have found that in the autumn-winter period, the level of the hormone gradually decreases and reaches its minimum values, after which it rises again (summer peak levels).

The level of sex hormones in women (estrogen, progesterone) also affects the concentration of thyroxine. During pregnancy, T4 is normally lowered. In men, the T4 indicator is stable, but after 40-45 years it begins to gradually decrease.

Symptoms of impaired T4 secretion

If the thyroid gland produces an insufficient amount of thyroxine or the hormone that regulates it (TSH - thyroid-stimulating hormone), then a person develops hypothyroidism. This disease is accompanied by clinical signs:

• dry skin and mucous membranes;
• weight gain;
• weakness, lethargy, decreased performance;
• hypersensitivity to temperature stimuli (to cold);
• violation of the menstrual cycle in women;
• problems with bowel movements (constipation);
• hair loss (alopecia);
• vascular-cardiac disorders (ischemic disease);
• coma (in advanced cases);
• cretinism, developmental delay in children.

If the gland produces too much T4, then the metabolism speeds up, the cells absorb energy faster. However, these changes cannot be considered positive - hyperthyroidism is also dangerous and is characterized by symptoms:

• increased heart rate (tachycardia);
• anxiety, nervousness, irritability;
• sleep disturbance (insomnia);
• tremor (trembling of the limbs);
• redness and dryness of the mucous membrane of the eyes;
• decreased visual acuity;
• weight loss (sudden weight loss);
• puffiness of the face, swelling of other parts of the body;
• indigestion.

In most cases, the balance of hormones is disturbed due to autoimmune pathologies: Graves' disease (hyperthyroidism with high free T4), Hashimoto's thyroiditis (hypothyroidism with low T4), etc.

Indications

• Confirmation of laboratory data when an increase or decrease in the level of TSH is detected;
• Diagnosis and monitoring of the effectiveness of the treatment of hypo- or hyperthyroidism;
• Scheduled medical examination (the study is carried out together with clinical blood and urine tests);
• Control of hormone therapy for diseases of the thyroid gland (analysis is prescribed 1 time per quarter);
• Examination of pregnant women with a history of thyroid disease. Violation of the production of thyroid hormones can lead to miscarriage, fetal fading, impaired physical or mental development of the fetus;
• Monitoring of babies born from mothers with diagnosed endocrine pathologies;
• Identification of the causes of infertility in women of childbearing age.

Normal values ​​of thyroxine

The reference values ​​of thyroxine are not sexually bound, but fluctuate depending on the age of the patient.

Free T4 in pregnant women

• 1st trimester: 12-19.5 pmol/l
• 2nd trimester: 9.5-17 pmol/l
• 3rd trimester: 8.5-15.5 pmol/l

T4 free increased

• Goiter, toxic and diffuse (enlargement of the thyroid gland);
• Thyroid dysfunction after childbirth;
• Therapy with synthetic hormone T4, including uncontrolled (self-medication);
• Thyrotoxic adenoma or myeloma (thyroid tumors);
• Hyperthyroidism (hyperfunction of the gland);
• TSH-independent thyrotoxicosis;
• Nephrotic syndrome (kidney damage, generalized edema throughout the body);
• Obesity;
• Liver disease (chronic form);
• Treatment with heparin, amiodarone, furosemide, danazol, valproic acid, tamoxifen, etc.

T4 free lowered

• Hypothyroidism (mainly congenital);
• Endemic goiter (pathology of the thyroid gland);
• Autoimmune diseases of the thyroid gland (thyroiditis);
• Cancer tumors localized in the thyroid gland;
• Operations in the area of ​​the gland, amputation of its individual parts;
• Iodine deficiency in the body;
• Sheehan's syndrome (death of pituitary tissue after childbirth, accompanied by bleeding and hypotension);
• A sharp decrease in body weight;
• Use of heroin and other drugs (hormones, oral contraceptives, anticonvulsants, lithium, steroids, etc.).

thyroxine in pregnant women

During pregnancy, the female body produces a large amount of sex hormones (estrogens, progesterone), which, in turn, stimulate the activity of the thyroid gland. At the same time, the secretion of transport globulins that bind thyroxin increases.

T4 directly affects the physical and mental development of the embryo. It is free thyroxine that is responsible for the formation of the fetal nervous system. Therefore, in an infant in the event of a lack of this hormone, the risk of congenital pathologies increases.

Determination of the total level of T4 during pregnancy is impractical, because. during this period, the production of binding proteins in the body is increased. In the results of the analyzes of a pregnant woman, thyroxin will always be higher than the reference values, which must be considered the norm.

Thyroxine (T4) is one of the two main hormones produced by the thyroid gland, which serves as a regulator of metabolism and energy metabolism in the body. The free form of T4 is the biologically active part of the total thyroxin, which affects the metabolism.

The main activity of the substance is to maintain a healthy form of the human body, namely:

• mental and nervous system;
• synthesis of building proteins;
• control over the cardiovascular system;
• a positive effect on the absorption of calcium, as well as assistance in its processing by bone tissues;
• metabolic management:
• participation in the physical progression of the body.

In addition to the direct effect of free thyroxine on the nervous system and mental abilities, it is also necessary in the process of cell development, maintaining their proper functioning.

Normal content

The T4 norm depends on two reasons: the age and general well-being of the patient. The standards for women are lower than for men.

Under what circumstances is analysis necessary?

The level of the hormone thyroxine is determined by taking a blood test from a vein. The procedure is prescribed for suspected thyroid diseases, as well as for pregnant women who had thyroid problems in the outpatient card. Under such circumstances, a newborn child may be subjected to this study, since there is a risk of hereditary predisposition to pathologies of the endocrine gland. Another category is girls suffering from infertility. Violation of the menstrual cycle is associated with a decrease in the amount of hormonal substances.

Behavior of the body during an increased value

Without any reason, T4 cannot rise, with the exception of bearing a child. Exceeding the norm is provoked for several reasons:

For an increased concentration of the hormone in the blood, the following symptoms are characteristic:

• excessive sweating and fatigue;
• irritability for no particular reason;
• sharp jumps in weight;
• tremor of hands and feet;
• cardiopalmus;
• arrhythmia.

The hormone thyroxine in an overestimated state "pushes" fats to break down faster than usual. This process affects the release of energy. Its excess adversely affects human organs, accelerating wear and tear.

If we consider the influence of "high" thyroxine from the point of view of the nervous system, then patients are characterized by mood swings (mainly negative emotions), trembling that occurs due to the contact of nerve signals with muscle fibers. With prolonged inactivity in this situation, calcium is gradually washed away, as a result, an abundance of bone fractures and osteoporosis.

Effect of low value

Decreased free thyroxine is the result of problems with the thyroid gland. In most cases, the development of hypothyroidism is inevitable.

The reasons that make doctors think about the low concentration of the hormone in the blood and send the patient to be tested:

• brain injury;
• inflammatory or tumor processes in the pituitary gland and hypothalamus;
• death of pituitary cells (Sheehan's syndrome);
• intervention of radioactive iodine or synthetic thyroxine in thyrotoxicosis;
• autoimmune thyroiditis;
• endemic goiter (congenital and acquired);
• Complete or partial removal of the thyroid gland.

Circumstances when none of the pathologies has been identified make one think about the appointment of an additional analysis - TSH.

As a result of the test, free thyroxine may drop below normal. However, when dealing with a low hormone value, laboratories often make mistakes in the study and a second procedure is required. Insufficiency of the thyroid gland haunts the patient throughout life.

Treatment is with the use of a thyroid hormone analogue. The dosage is calculated based on the needs of the body and is planned by the attending physician based on the results of the test according to an individual program.

Pregnancy

Thyroid hormones serve as a kind of protector of the fetus, protecting it from intrauterine death, and also affect the formation and growth of the fetus. Failure in the work of this body will necessarily entail disastrous consequences. The child is born unhealthy, such syndromes as Down and cretinism are possible, and the birth itself may begin prematurely.

To avoid such a fate for the unborn child, women are routinely screened for thyroid hormones. This procedure cannot be ignored, because running hypothyroidism during gestation threatens to lose the baby.

Diagnosis includes donating blood for tests:

1. free thyroxine (T4);
2. free triiodothyronine (T3);
3. thyroid-stimulating hormone (TSH).

As already mentioned, thyroxine T4 affects the development of the fetus, in particular, the bone marrow and brain. Also affected are blood vessels, the reproductive system, skeletal muscles, and the heart. Deciphering the result of the study is carried out by an obstetrician-gynecologist or an endocrinologist-gynecologist.

With destabilization of thyroid hormones, you should immediately start taking corrective drugs. Early term is doubly dangerous. It was then that the fetus was just beginning to form, and even a delay of several days could affect its development.

The chronic form of T4 deficiency involves the use of artificial thyroxin until the very birth. In children born with a disturbed hormonal background, congenital hypothyroidism or hyperthyroidism occurs. The consequence of hypothyroidism is a systemic failure in development and the ensuing cretinism. Below is a table of hormonal norms during pregnancy.

Treatment Adjustment

The lower level of thyroid hormones requires special therapy, which consists in oral administration of a synthetic hormone. The dosage for each is individual and is prescribed by an endocrinologist. Patients using these medications should be tested for free thyroxine and TSH at least once a year.

The main danger, along with side effects, with such treatment is prolonged, uncontrolled use of drugs. There are cases when the functionality of the gland is restored after a certain time, and the person continues drug therapy. This state of affairs adversely affects health.

Elevated thyroxine can cause an overdose of the drug and the occurrence of hyperthyroidism. In what cases it is necessary to control the hormonal system?

• Euthyroid goiter and euthyroid cyst compresses the gland, which cannot but affect the well-being and hormonal state of a person;
• Toxic formations in the thyroid gland. Restoring the level of the hormone with nodes, cysts, goiter, it is necessary to periodically take a blood test;
• Strumectomy is the complete or partial removal of the thyroid gland by surgery. The consequence of such an operation is a long-term use of thyroxin. In some cases, it will have to be accepted. Dose adjustment occurs after testing;
• Deficiency of iodine in the patient's region of residence or the absence of this substance in the daily diet. Lack of iodine disrupts the connective processes of T4 and other thyroid hormones;
• Heat stroke, hypothermia, poisoning - all these factors serve as a catalyst for the occurrence of hypo- or hyperthyroidism;
• Pregnancy and before menopause. Based on statistical calculations, the main part of diseases associated with the thyroid gland overtakes women after 35 years. In girls in position, the load on the gland increases many times over. For this reason, a benign form of hyperplasia is often detected.

The correct diet, as well as the daily routine, contribute to the adequate functioning of the thyroid gland. Take care of your health, go in for sports and be happy!

T4 - thyroid hormone produced by cells of the thyroid follicles. Thyrocytes synthesize thyroglobulin from the amino acid and iodine, which is a precursor of thyroxine. Thyroglobulin accumulates in the follicles, and if necessary, thyroxine is formed from it by division into fragments.

The main action of the hormone T4 is to accelerate catabolism - the process of obtaining energy from energetically significant metabolites (glycogen, fat). An excessive concentration of thyroxine in the blood leads to palpitations, irritability, and weight loss. But this does not mean that the hormone is harmful, these are just symptoms of its overdose. Normally, tetraiodothyronine maintains the tone of the nervous system, pulse rate and adequate metabolism.

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

Hormones T3, T4 are also called thyroid hormones., since they are distinguished by, referred to in Latin as "thyroid". TSH is also sometimes referred to as thyroid, but this is erroneous, because it is formed by the pituitary gland, located in the brain, and controls the hormone-forming function of the gland.

Often, along with a blood test for the hormones TSH, T3, T4, antibodies to TPO and thyroglobulin are simultaneously determined. Typically, endocrinologists use these indicators to diagnose thyroid pathologies. Sometimes thyroid hormones are examined during the treatment of a disease in order to determine its dynamics and the effectiveness of the prescribed therapy. This article will provide information about what the T4 hormone is, what functions it performs in the body, and how the analysis of its content is interpreted.

The T4 hormone belongs to the group of iodine-containing thyroid hormones. Its chemical formula contains two tyrosine amino acid residues and four iodine halogen atoms. T4 hormones are synonymous with tetraiodothyronine and thyroxine. The substance got its name because of the number of iodine atoms contained in the molecule. Due to the simple structure, the concentration of tetraiodothyronine can be easily determined in the laboratory. For the same reason, the hormone can be synthesized artificially, which is used in hormone therapy.

Hormone T4 in the blood

In the bloodstream, the T4 hormone is found mainly in a protein-bound state. When thyroxine is formed in the thyroid follicles, it is captured by a special protein - thyroxine-binding globulin (TSG). This substance performs a transport function, delivering the hormone to the cells of the body. That small amount of non-protein-bound thyroxine is called free T4. It is this fraction that is responsible for providing the biological effect. The part of the hormone that is associated with TSH is called T4 bound. If you separately determine free and bound T4 in the blood, and then add these values, you get total T4.

In the body, free thyroid hormones (free T4, free T3) have the main effect, so their content is of the greatest importance for determining thyroid pathologies. In laboratories, most often they conduct a blood test for thyrotropin and free T4. The TSH indicator is used to assess the regulation of the thyroid gland by the pituitary gland, and free T4, as the main hormone of the gland, directly reflects its function. The concentration of free T4 is elevated in hyperthyroid states or as a result of an overdose of hormonal agents used for therapy.

In the clinical practice of endocrinologists, the analysis of TSH, T4 hormones is the most commonly used diagnostic method. Hormonal studies are prescribed in various combinations, taking into account the symptoms and economic possibilities of the patient.

At the initial visit to the endocrinologist, if the patient has no pronounced symptoms, it may be enough to take an analysis for the hormones TSH, T4, T3. As for the last two hormones, it is better to investigate their active, i.e., free fractions. In cases where a patient receives thyreostatics for the treatment of an early stage of Graves' disease (diffuse toxic), it is better to determine only free hormones T3 and T4. Under the action of thyreostatic drugs, these indicators rapidly decrease, while the TSH level seems to be late and does not have time to decrease.

If a patient has been treated for a long time for insufficient gland function, then for periodic monitoring of the quality of therapy, it is sufficient to determine only the concentration of thyroid-stimulating hormone (TSH). Free T4 is examined only if there are special indications. You should know that in the case of taking thyroxin, a blood test for the hormone T4 can be taken only before taking it. If this rule is not observed, the result of the analysis will be uninformative, since the amount of thyroxine that came with the medication will be added to the T4 hormone secreted by the thyroid gland.

During pregnancy, the value of free hormone T4 especially increases, because the level of thyrotropin can be reduced as a result of the action of hCG - human chorionic gonadotropin produced by the placenta. Therefore, when examining pregnant women, the determination of TSH alone is insufficient for a correct diagnosis. It is necessary to take tests simultaneously for TSH and T4.

In the direction or form with the result of the study, you can find various abbreviations:

FT4, FT3 - T4 and T3 free (English free, which means "free");

Hormone St. T4, St. T3 are also free forms of hormones.

What is the norm of the hormone T4?

Free hormone T4. To correctly evaluate the results of the analysis for the free hormone T4, it is not enough to know any specific norms. The normal content of thyroxine largely depends on the laboratory conducting the analysis. For different analyzers, these indicators are different, even the set of reagents used in each case matters. As a rule, the permissible concentration of T4 in the blood is indicated on the form after the result of the analysis. When using high-quality laboratory equipment of the 3rd generation in healthy people, the concentration of thyroxin ranges from about 9 to 20 pmol / l.

Total hormone T4. Such an indicator as the total hormone T4 depends on the physiological state of the body. For example, in pregnant women it rises. Therefore, the limits of the norm for total thyroxine are more variable than for its free fraction.

T4 hormone (tetraiodothyronine) total

T4 hormone (tetraiodothyronine) free

Hormone T4 is elevated

The following symptoms are characteristic of an excess content of the T4 hormone:

increased sweating,

fatigue,

Irritability,

Rapid pulse and feeling of increased heartbeat,

Increased T4 hormone accelerates the breakdown of fats in the body, therefore, body weight decreases. An excess amount of released energy has a negative impact on the functions of the organs. This is manifested in the acceleration and strengthening of the work of the heart, increased sweating. Overstimulation of the nervous system causes irritability and frequent mood swings, and the acceleration of neuromuscular transmission leads to tremors in the limbs. Weight loss in this condition is not physiological, because it occurs against the background of a violation of the functions of internal organs. With prolonged preservation of an increased concentration of thyroxin, calcium is washed out of the bones, which is fraught with an increased risk of and.

Reasons for increasing the hormone T4 (total and free):

Myeloma with high levels of immunoglobulin G;

Postpartum thyroid dysfunction;

Acute and subacute thyroiditis;

Taking synthetic analogues of thyroid hormones, cordarone, methadone, oral contraceptives, radiopaque iodine-containing substances, prostaglandins, tamoxifen, insulin, levodopa;

porfiria

Low T4 hormone is usually characteristic of insufficient hormonal function of the thyroid gland. This pathology is called hypothyroidism.

The reasons for low levels of the hormone T4 include the following conditions:

Treatment of thyrotoxicosis with thyreostatics or radioactive iodine;

Autoimmune thyroiditis (antibodies are produced in the body against cells of thyroid follicles, which leads to insufficient production of thyroxine);

Removal of the gland or part of it by surgery.

There are times when in apparently healthy people, the free hormone T4 is lowered. Most often this is due to errors in the performance of research in the laboratory. When rechecked in better laboratory centers, it turns out that the concentration of thyroxine is normal. To avoid errors in the diagnosis, it is necessary to take into account the clinical picture and the significance of the TSH level. In all cases, when the T4 hormone is lowered in the analysis, and the TSH hormone is within the normal range, the result should be interpreted with caution and, if possible, re-tested.

If a recheck in a good laboratory again showed a reduced level of thyroxine, you should contact an endocrinologist. Insufficiency of thyroid gland function, as a rule, is lifelong. Therefore, continuous therapy with the appointment of a synthetic hormone T4 is necessary. The artificially obtained thyroxine is identical in structure to the natural hormone and, with the right dosage, does not cause any side effects.

Causes of a decrease in the hormone T4 (total and free):

Sheehan's syndrome;

Congenital and acquired;

Traumatic brain injury;

Inflammatory processes in the pituitary gland and hypothalamus;

Treatment with tamoxifen, antithyroid drugs (mercasolil, propylthiouracil), steroids and anabolics, beta-blockers (metoprolol, propranolol), NSAIDs (dictofenac, ibuprofen), statins (atorvastatin, simvastatin), anti-tuberculosis and anticonvulsant drugs, diuretics, lithium salts, radiopaque substances.

Hormone T4 during pregnancy

The level of thyroxin plays a very important role in the development of the fetus. The free hormone T4 in the first 3 months of pregnancy ensures the development and growth of the nervous system of the embryo, so its deficiency can lead to various congenital pathologies. 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. In a pregnant woman, there is a physiological increase in the synthesis of thyroxin-binding globulin, and it binds most of the T4 in the bloodstream. The determination of total T4 during this period is uninformative, since its value will invariably be increased, despite the fact that the free fraction of the hormone is normal.

During pregnancy, you need to donate free hormone T4, this indicator 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, which does not require treatment. But if this indicator significantly exceeds the upper limit, it is necessary to reduce the indicator by drug therapy. Treatment is carried out very carefully, under the constant control of thyroxine, to ensure the normal development of the fetus.

Education: Diploma of the Russian State Medical University N. I. Pirogov, specialty "Medicine" (2004). Residency at the Moscow State University of Medicine and Dentistry, diploma in Endocrinology (2006).

We often see in the results of the analysis hormones TSH, T3, T4, often with antibodies to TPO and thyroglobulin. These tests are done when a thyroid disease is suspected, and sometimes during treatment for a thyroid disease, in order to monitor the results. Let's try to figure out what the T4 hormone is responsible for in the human body, what functions it performs, how to determine it in the blood, and how to understand the results of the tests.

Hormone T4 is a hormone from the group of iodothyronines, built on the basis of two residues of the amino acid tyrosine and four iodine atoms. Synonyms: thyroxine, tetraiodothyronine. It is because of the number of iodine atoms that the hormone T4 received its numerical designation. The structure of the hormone is very simple, it can be quite simply synthesized artificially and just as easily detected in the blood by laboratory analyzers.

T4 - thyroid hormone produced by its cells. Thyroid cells (thyrocytes) capture amino acids and iodine and synthesize from them the precursor of thyroxin - thyroglobulin, which is stored in the thyroid tissue in special storages - follicles. When there is a need for the T4 hormone, thyroglobulin is cut into short fragments and released into the blood - already in the form of the finished T4 hormone.

The main action of the hormone T4- catabolic, i.e. releasing energy from energy substrates accumulated in the body (fat, glycogen, etc.). What kind of free T4 hormone can be easily understood if you start taking 200 or 300 micrograms of this hormone per day - against the background of taking this medication, the pulse will quicken, irritability will appear, and weight loss will begin. From this experiment (by the way, it is regularly carried out by hundreds and thousands of women in search of a way to lose weight), it does not follow, of course, that thyroxine is harmful, since only the symptoms of an overdose of the T4 hormone look like this, and normally it only ensures the normal breakdown of fats, normal heart rate , normal nervous excitability.

It should be noted that in the body T4 hormone is not the most active thyroid hormone, it is almost 10 times less active than the hormone T3 - triiodothyronine, containing 3 iodine atoms. In a small amount, T3 is formed by the cells of the thyroid gland, and its main amount is created from the hormone T4 directly in the tissues of the human body (there is, as it were, activation of a previously not very active hormone).

Hormones T3, T4 are also called thyroid hormones.(from the word "thyroid" - the thyroid gland), since they are formed in the thyroid gland. You should also know that the hormones TTT and T4, often referred to as "thyroid hormones TSH, T4", are actually produced in completely different places - TSH is produced in the pituitary gland at the base of the brain, and T4 is secreted by thyrocytes (thyroid cells) . Patients get used to the fact that when they turn to an endocrinologist, they are often prescribed TSH and T4 at the same time, and therefore they combine them together, which is generally not true.

Hormone T4 in the blood

In blood the T4 hormone is mainly in a protein-bound state. There is a special transport protein - thyroxin-binding globulin (TSG), the main function of which is to capture the thyroxine molecule and deliver it to various parts of the human body. As soon as the T4 hormone is produced by the thyroid gland, it is immediately taken up by the TSH molecule. Only a small part of T4 is in a state not bound to the protein - it is called the “free T4 hormone”. It is this part of the hormone that has the main biological effects. If you measure the level of protein-bound T4 hormone with an analyzer and, together with it, the level of free T4, combining all the values ​​\u200b\u200bin one, you get an analysis for the T4 hormone overall.

Due to the fact that the main action is provided by free thyroid hormones (T4 free, T3 free), and it is recommended that they be determined during the analysis - so the analysis will be more accurate and will be more consistent with the real clinical situation. That is why the hormones TSH and T4 are most often given in laboratories: the first one is the hormone controlling the thyroid gland, the second one is the main thyroid hormone.

The level of free T4 hormone increases with hyperthyroidism - an increased function of the thyroid gland, or with an overdose of hormonal drugs.

T4 hormone analysis

Analysis for hormones TSH, T4- one of the most commonly used in the clinical practice of an endocrinologist. These tests can be prescribed in various combinations in order to save the patient's money and at the same time obtain enough data to make a diagnosis and prescribe treatment.

At the first examination of the patient, if he does not have expressed complaints, quite often get tested for TSH, T4, T3 hormones(It is desirable to donate free hormones T4 and T3).

If a patient is being treated at an early stage of diffuse toxic goiter (Graves' disease), when there is a rapid decrease in hormone levels with special drugs - thyreostatics, it is best to take only hormones T3, T4(also optimally - free), since the TSH hormone will not "have time" to change with frequent determination (it changes rather slowly).

With long-term treatment of reduced thyroid function with a synthetic analogue of T4 - thyroxin, when the level of hormones has already been observed by a doctor for quite a long time, it is often enough to donate blood only for TSH. T4 free is given in such situations only at the special request of a doctor. It is important to remember that in the case of taking thyroxine, a blood test for the hormone T4 can be taken only before taking the thyroxine tablet. The hormone thyroxine in a tablet and the hormone T4 in the blood are absolutely the same, so determining the level of T4 after taking a thyroxine tablet will only allow you to measure how much thyroxine you took before the analysis.

During pregnancy, the value of the hormone free T4 especially increases, since TSH can even be reduced (its level decreases due to the production of human chorionic gonadotropin, hCG, in the placenta, which performs the same functions as TSH and “takes over” part of its work). Therefore, pregnant women need to take hormones TSH, free T4 (one TSH is already not enough).

In the results of a blood test, you can often find abbreviations:

- hormone St. T4, St. T3(meaning free hormones);

- FT4, FT3(also refers to free hormones, from English free = free).

Hormone T4 - the norm

For a test like hormone T4 free, the norm entirely depends on the laboratory in which the blood test was performed. The rate of hormones T3, T4, TSH depends on the equipment used in the laboratory, and even on the set of reagents used, so there is no need to remember the standards now - in high-quality laboratories, the rate is always indicated immediately after the result of the study.

When measuring the level of the free T4 hormone in pmol / l on high-quality equipment of the 3rd generation, its level is about 9-19 pmol / l.

Hormone T4 total- its norm may depend on the condition of the patient. For example, during pregnancy, the level of total T4 rises, and this increase is normal, physiological. That is why the rate of the total T4 hormone has a greater variation than the rate of the free hormone.

Hormone T4 is elevated

If the hormone T4 free increased symptoms usually include:

sweating,

Irritability,

fatigue,

increased heart rate,

The appearance of a feeling of "interruptions" in the region of the heart,

Trembling (tremor) of the hands,

Weight loss.

Elevated T4 hormone causes an increase in the breakdown of energy substances in the body, the release of excess energy. As a result, the amount of body fat begins to decrease, and the excessively allocated energy is directed to other parts of the human body, enhancing physiologically normal reactions to an unacceptably high level: normal excitability is replaced by irritability, normal heart rate - tachycardia (accelerated pulse), the normal reaction rate of the nerves changes to excessive - there is even a trembling of the fingers. As a result, a person loses weight, but this weight loss cannot be called physiological and beneficial - it occurs at the cost of dysfunction of the heart and nervous system. If the elevated T4 hormone persists for a long time, the weakening of the bone tissue increases, osteoporosis occurs, and the risk of fractures increases.

Hormone T4 is lowered

Low T4 hormone occurs primarily in hypothyroidism (insufficient thyroid function).

Causes low levels of T4 hormone can be:

Removal of the thyroid gland during surgery;

The development of autoimmune thyroiditis (inflammation of the thyroid gland of an immune nature, leading to a lack of T4 hormone);

Treatment of excessive thyroid function in toxic goiter with thyreostatics with the occurrence of an overdose;

Consequences of treatment of thyrotoxicosis with radioactive iodine.

At the same time, in St. Petersburg, there is often a situation when in blood tests in apparently perfectly healthy people, the free T4 hormone is lowered. The reasons for this lie in the mistakes of the laboratories. One of the largest laboratory services in St. Petersburg and the Leningrad region (for ethical reasons, we cannot indicate the name of this laboratory within the framework of this article) extremely often reports that the T4 hormone is below normal, and it is the free T4 hormone. Rechecking this fact, carried out by employees of the North-West Endocrinology Center in the reference laboratory of the 3rd generation of the German laboratory network LADR in several hundred cases, almost always revealed a normal level of free T4 hormone in the blood. Suspicions that the blood test was performed with an error should arise first of all in all cases when the T4 hormone is lowered in the analysis, and the TSH hormone is within the normal range- similar changes in hormone levels are possible, but only in very rare cases.

If a decrease in T4 hormone is confirmed by testing in a quality laboratory, you should contact an endocrinologist. Perhaps we are talking about a decrease in thyroid function, which most often has a long-term (lifelong) character and requires treatment with a synthetic preparation of the T4 hormone - thyroxine, which completely repeats the molecule of the natural hormone and has absolutely no side effects.

Hormone T4 during pregnancy

Hormone T4 free during pregnancy acquires special significance - it is its level that determines the rate of brain development in a developing child. In the first three months of intrauterine development, it is the T4 hormone that affects the maturation of the nervous system. The norm in women for this hormone is similar to the norm for men, however, during pregnancy, the total hormone T4 is not recommended to be determined, since it will almost always be elevated. The fact is that during pregnancy, the production of thyroxin-binding globulin increases, which binds the vast majority of T4 in the blood. In the protein-bound state, the T4 hormone is not active, so the seemingly dangerous increase in the level of total T4 hormone during pregnancy has absolutely no clinical significance.

During pregnancy, it is necessary to donate free T4 hormone- its norm should be maintained especially clearly. Slight increases in free T4 levels are possible, often they do not even need to be treated, however, a decrease in free T4 levels during pregnancy should be approached very carefully, and correction of thyroid hormone levels should be carried out immediately to ensure optimal development of the child.

Analysis for the hormone T4 at the North-West Endocrinology Center

The North-Western Center of Endocrinology measures the level of T4 hormone (total and free) in the blood using the state-of-the-art 3rd generation immunochemiluminescent laboratory of the Russian division of the German laboratory network LADR. To determine the level of the T4 hormone, analyzers Abbott Architect (USA) and Advia Centaur (Germany) are used, which allow performing analyzes with the utmost accuracy.

You can take a blood test for the T4 hormone in St. Petersburg and Vyborg at the addresses of the center's outpatient branches:

- Petrograd branch(located in the center of St. Petersburg, 200 meters to the left from the Gorkovskaya metro station; address - Kronverksky pr., 31, tel. 498-10-30, from 7.30 to 20.00, seven days a week; parking is available);

- Primorsky branch(located in the Primorsky district of St. Petersburg, Savushkina st., 124, building 1, tel. 344-0-344, from 7.00 to 20.00, seven days a week; parking is available);

- Vyborg branch(Vyborg, Pobedy Ave., 27A, tel. 36-306, from 7.30 to 20.00, seven days a week, there is parking).

Pre-registration for a blood test is not required. In the branches of the center, you can take tests for both an adult and a child - treatment rooms are specially equipped for taking blood test for hormones TSH, T3, T4 in children.

• Thyrotoxicosis

  Thyrotoxicosis (from the Latin "glandula thyreoidea" - thyroid gland and "toxicosis" - poisoning) is a syndrome associated with excessive intake of thyroid hormones into the blood.

• Nodular toxic goiter

  Nodular toxic goiter is a disease accompanied by the appearance of one or more thyroid nodules with functional autonomy, i.e. capable of intensively producing hormones, regardless of the real needs of the body. In the presence of several nodes, they usually talk about multinodular toxic goiter.

• Basedow's disease (Graves' disease, diffuse toxic goiter)

  The cause of Graves' disease lies in the malfunctioning of the human immune system, which begins to produce special antibodies - an antithet to the TSH receptor, directed against the patient's own thyroid gland.

• Hormone T3

  Hormone T3 (triiodothyronine) is one of the two main thyroid hormones and the most active of them. The article tells about the structure of the T3 hormone molecule, a blood test for the T3 hormone, types of laboratory parameters (free and total T3 hormone), interpretation of the test results, and where it is better to donate thyroid hormones

• thyroglobulin

  Thyroglobulin is the most important protein found in thyroid tissue, from which the thyroid hormones T3 and T4 are produced. Thyroglobulin level is used as the main marker of recurrence of differentiated thyroid cancer (follicular and papillary). At the same time, thyroglobulin is often given without indications - this increases the costs of patients. The article is devoted to the significance of thyroglobulin, indications for taking an analysis for thyroglobulin and evaluating the results.

• Autoimmune thyroiditis (AIT, Hashimoto's thyroiditis)

  Autoimmune thyroiditis (AIT) is an inflammation of the thyroid tissue caused by autoimmune causes, which is very common in Russia. This disease was discovered exactly 100 years ago by a Japanese scientist named Hashimoto, and since then has been named after him (Hashimoto's thyroiditis). In 2012, the global endocrinological community widely celebrated the anniversary of the discovery of this disease, since from that moment endocrinologists have the opportunity to effectively help millions of patients around the planet.

• Thyroid hormones

  Thyroid hormones are divided into two distinct classes: iodithyronins (thyroxine, triiodothyronine) and calcitonin. Of these two classes of thyroid hormones, thyroxine and triiodothyronine regulate the body's basal metabolism (the level of energy consumption that is necessary to maintain the body's vital functions in a state of complete rest), and calcitonin is involved in the regulation of calcium metabolism and bone tissue development.

  Operations on the thyroid gland

  The North-Western Center of Endocrinology is the leading institution of endocrine surgery in Russia. Currently, the center performs more than 5,000 operations on the thyroid gland, parathyroid (parathyroid) glands, and adrenal glands annually. In terms of the number of operations, the North-West Endocrinology Center steadily ranks first in Russia and is one of the three leading European endocrine surgery clinics

• Endocrinologist's consultation

  Specialists of the North-Western Center of Endocrinology diagnose and treat diseases of the endocrine system. The endocrinologists of the center in their work are based on the recommendations of the European Association of Endocrinologists and the American Association of Clinical Endocrinologists. Modern diagnostic and therapeutic technologies provide optimal treatment results.

• Expert ultrasound of the thyroid gland

  Ultrasound of the thyroid gland is the main method to assess the structure of this organ. Due to its superficial location, the thyroid gland is easily accessible for ultrasound. Modern ultrasound devices allow you to examine all parts of the thyroid gland, with the exception of those located behind the sternum or trachea.