Free T4 - what is this hormone?
The content of the article:
- What is free T 4 hormone responsible for in women and men
- Why the hormone T 4 can be increased
- Why T 4 can be lowered
- Imbalance symptoms
- Diagnostics
- T 4 free: norm
- Video
To answer the question of whether T 4 is free - what kind of hormone it is, first you need to determine what thyroxine is. This biologically active substance belongs to the main forms of thyroid hormones of the thyroid gland and is synthesized by its follicular cells. The production of thyroxine is controlled by the pituitary thyroid stimulating hormone (TSH). Thyroxine is biologically inactive, in peripheral tissues it turns into a more active form - triiodothyronine (T 3). 1 thyroxine molecule contains 4 iodine atoms. A significant part of this hormone circulates in the bloodstream in a bound form, in conjunction with thyroxine-binding globulin. An insignificant part of thyroxine is in the blood in free form.
Thyroxine is one of the thyroid hormones that plays an extremely important role in the body
Free thyroxine (free T 4, free T 4, CT 4, free tetraiodothyronine) is a fraction of the thyroid hormone circulating in the blood, which is not bound to proteins and is approximately 0.03% of the total thyroxine concentration. The free fraction of thyroxine most adequately characterizes the hormonal function of the thyroid gland.
What is free T 4 hormone responsible for in women and men
There are no specific target cells for this hormone in the body, thyroxine affects all tissues of the human body. It is able to penetrate the membrane and bind to the receptors of any cells, as well as accumulate in the tissues of the thyroid gland. The mechanism of release of this substance from the thyroid gland is regulated by its concentration in the blood.
Among the main tasks of this hormone in the body is the activation of metabolic processes, it is necessary to ensure the development and differentiation of all cells in the body.
In addition, it performs the following functions:
- controls the growth and development of the body;
- increases body temperature;
- stimulates protein synthesis;
- increases heart rate;
- thickens the lining of the uterus in women;
- stimulates the metabolism of vitamins;
- lowers the level of cholesterol, triglycerides in the blood;
- increases the excretion of calcium in the urine;
- increases oxygen consumption by tissues (except for the brain, spleen, testes in men).
Why the hormone T 4 can be increased
A high level of free thyroxine can be observed in inflammatory diseases and neoplasms of the thyroid gland, liver and kidney disorders. In addition, it can increase in women during pregnancy.
An increase in thyroxine levels can be caused by:
- hyperthyroidism;
- choriocarcinoma;
- multiple myeloma;
- acquired immunodeficiency syndrome;
- hepatitis;
- postpartum thyroid dysfunction;
- obesity.
Radiological contrast agents, oral contraceptives, antiepileptic drugs, insulin use, and large doses of acetylsalicylic acid can increase the level of the hormone.
Why T 4 can be lowered
After the age of 40, thyroxine levels usually begin to decrease in both men and women. A temporary decrease in the level of the hormone is possible with excessive physical exertion. Surgical removal of the thyroid gland leads to a permanent decrease in the thyroxine content.
In addition, when a low concentration of thyroxine is found, it means that one of the following pathological conditions is possible:
- hypothyroidism;
- loss of protein (in diseases of the gastrointestinal tract, nephrotic syndrome);
- Itsenko-Cushing's disease;
- pathology of the hypothalamus and / or pituitary gland;
- iodine deficiency in the body.
Illegal drugs and drugs of the following groups can reduce the hormone content:
- glucocorticoids;
- antibiotics;
- anticonvulsants;
- anabolic steroid;
- non-steroidal anti-inflammatory drugs;
- diuretics;
- anti-tuberculosis;
- beta-blockers.
Imbalance symptoms
Both insufficient and overactive thyroid gland can be accompanied by its enlargement.
A low concentration of thyroxine is characterized by:
- increase in body weight;
- dry skin;
- fatigue even with minor physical exertion;
- menstrual irregularities in women.
A congenital lack of this substance in the body in young children can lead to the development of cretinism, in older patients - myxedema.
If there are signs of hormonal imbalance, you need to see a doctor
With a high level of free thyroxine fraction, the following can be observed:
- tachycardia;
- arrhythmia;
- swelling on the face;
- weight loss;
- sleep disorders;
- exophthalmos;
- tremor of the upper and lower extremities;
- increased sweating;
- feeling anxious;
- irritability.
With a long-term elevated content of thyroxine in the blood, a person begins to wash out calcium from the bones, which increases the risk of fractures and the development of osteoporosis. If, with an increased production of thyroxine, the patient develops hyperthyroidism, this may cause the development of heart failure.
Diagnostics
To obtain information about the functioning of the thyroid gland, an analysis for thyroxine is prescribed in combination with a laboratory determination of the level of thyroid-stimulating hormone (especially with fluctuations in the level of thyroxine-binding globulin during pregnancy, in the case of androgen and estrogen preparations) and triiodothyronine. The main functions in the body are performed by free fractions of thyroxine and triiodothyronine. The study of antibodies to thyroid peroxidase and thyroglobulin is of diagnostic value.
Rules for preparing for blood donation for analysis:
- If the patient uses thyroxin preparations, it is possible to donate blood for analysis only before taking it, otherwise a distorted result will be obtained.
- On the day preceding blood donation, stress and excessive physical activity should be excluded.
- Before analysis, fatty foods must be removed from the diet.
- It is recommended to donate blood in the morning on an empty stomach (after the last meal, at least 8 hours should pass).
Different laboratories may use different research methods, the norms for the content of thyroxine in the blood may differ, in addition, different laboratories may use different units for measuring the concentration of free thyroxine in the blood (pmol / l, ng / dl, ng / l, pg / ml and etc.), which you should also pay attention to. If it is necessary to repeatedly determine the indicators of thyroid function, it is best to take tests at the same medical institution.
T 4 free: norm
In women, the concentration of thyroxine in the blood is usually slightly lower than in men. During normal functioning of the thyroid gland, the content of free T 4 in the blood depends on the level of thyroxine-binding globulin.
Daily fluctuations are characteristic. So, the highest level of the hormone is observed between 08:00 and 12:00, the lowest - in the period from 23:00 to 03:00. There are also seasonal changes in the level of free T 4 in the blood: the maximum concentration is between September and February, the minimum value is in the summer months.
The table shows normal blood levels of the free thyroxine fraction.
| Patient category | Reference values, ng / dl |
| Non-pregnant women and men | 0.89-1.76 |
| Pregnant women (I trimester) | 0.86-1.87 |
| Pregnant women (II-III trimester) | 0.64-1.92 |
The endocrinologist should decipher the analysis result. The treatment regimen (if necessary) is selected depending on the cause of the development of the pathology. Self-medication is unacceptable.
Video
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Anna Aksenova Medical journalist About the author
Education: 2004-2007 "First Kiev Medical College" specialty "Laboratory Diagnostics".
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