Free T4 in women: table of age norms, causes of deviations
The content of the article:
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Table of norms of T4 free in women
- Normal Free T4 Values in Women
- Normal Free T4 Values in Pregnant Women
- What is T4 free
- Laboratory research
- Indications for the determination of free T4
- When T4 free is above normal
- When T4 free is below normal
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Tactics for deviation of T4 free from the norm
- Treatment with an increase in T4 free
- Treatment with a decrease in free T4
- Conclusion
- Video
In the female body, thyroid hormones affect all types of metabolism, the menstrual cycle and gestation. Thyroxine (T4) is one of two thyroid hormones synthesized by the thyroid gland. Two forms of thyroxine circulate in the blood - free (T4cw, fT4) and bound to proteins. For the diagnosis and treatment of various disorders, it is necessary to study and assess T4 free in women, the table of norms by age allows you to do this quickly.
Free T4 is a protein-free fraction of thyroxine, the level of which in the blood depends on age
Table of norms of T4 free in women
In the course of laboratory diagnostics, the content of total and free T4 is determined. Both indicators provide an indication of thyroid function. However, there are conditions (pregnancy, renal failure, liver disease, taking certain medications) in which the properties and concentration of transport proteins change. Under these conditions, the study of the free T4 level acquires especially great diagnostic value.
Normal Free T4 Values in Women
| Age period | Reference interval | unit of measurement |
| Newborn | 10.0-22.0 | pmol / l |
| Children under one year old | 8.0-17.0 | pmol / l |
| 1-5 years | 9.0–20.0 | pmol / l |
| 6-14 years old | 8.0-17.0 | pmol / l |
| 15-18 years old | 8.5–20.6 | pmol / l |
| Adults under 55 | 9.0-22.0 | pmol / l |
| After 55 years | 6.0-18.0 | pmol / l |
The average indicators of thyroxine, not bound to proteins, in women and men practically do not differ. But women have a physiological period when concentration fluctuations are significant.
Normal Free T4 Values in Pregnant Women
When carrying a fetus, the level of free thyroxine depends on the duration of pregnancy.
| Trimester | Reference interval |
| First | 10.3-15.5 pmol / l |
| Second | 7.7-12.9 pmol / l |
| Third | 6.4-0.3 pmol / l |
The increase in average values in the period up to 12-13 weeks is due to an increase in the amount of thyroxine-binding protein and the stimulating effect of human chorionic gonadotropin. This hormone is structurally similar to T4. The reason for the decrease in the level by the end of pregnancy is the hormonal activity of the placenta and the more intense attachment of thyroxine to transport globulins. If the analyzes are submitted correctly, and the deviations do not go beyond the permissible interval, then no correction is required.
What is T4 free
What is T4 hormone responsible for in women? Under the control of thyroid-stimulating hormone (TSH) of the pituitary gland, iodothyronines - thyroxine and triiodothyronine (T3) - are produced in the thyroid gland. T4 is the leading form of thyroid hormone and the basis for the formation of T3.
In the blood, most of the T4 binds to special transport proteins and only about 0.04–0.05% remains in a free state. This fraction also has hormonal activity. The bound thyroxine enters the tissues, where its main part, losing the iodine atom, turns into T3.
Laboratory research
The maximum concentration of the T4 hormone is observed in the morning. It is necessary to donate blood for research at the same time. Sample collection requirements are standard:
- Stopping food intake 8 or more hours before the examination.
- The exclusion of the use of alcoholic beverages 12 or more hours before donating blood.
- Abstaining from smoking 2-3 hours before going to the laboratory.
- Refusal to conduct immediately before the manipulation of x-ray examination, electrophoresis, UHF and massage.
Recommendations to stop taking thyroid hormones a few days in advance are not always justified. If the determination of the level is carried out for the purpose of diagnosis, then usually such means have not yet been assigned. In the case of dynamic observation of treatment, tests are taken to adjust the dose, and discontinuation of the dose may distort its selection. Therefore, the decision to refuse medications should be made by a doctor.
Indications for the determination of free T4
The analysis for free T4 is rarely carried out independently, usually in parallel the content of several hormones in the blood serum that characterize the work of the thyroid gland is determined. These include: thyroid-stimulating hormone, total and free triiodothyronine, antibodies to thyrocyte peroxidase, thyroglobulin, thyrotropin receptors. The specific list is determined by a specialist. The examination is prescribed if:
- complaints inherent in hypothyroidism (apathy, fatigue, deterioration in performance, memory, drowsiness, chilliness, weight gain on the background of decreased appetite, swelling, dry hair and skin, tendency to constipation, rare pulse, hypotension);
- symptoms of hyperthyroidism (emotional lability, irritability, rapid pulse, increase in blood pressure, sweating, enlargement of the thyroid gland, weight loss due to increased appetite, loose stools, violation of the monthly cycle);
- the need to monitor the effectiveness of hormone therapy in any thyroid pathology;
- changes in the level of thyroid-stimulating hormone revealed during a preventive examination;
- long-term use of combined oral contraceptives;
- necessary when planning pregnancy;
- infertility;
- disruptions in the menstrual cycle;
- habitual miscarriage;
- complicated course of pregnancy.
The interpretation of the results is carried out by the attending physician, but a general understanding of the possible causes of changes is also necessary for the patients.
When T4 free is above normal
The study may show an increase in the concentration of thyroxine, not associated with proteins, in a number of diseases and conditions of the woman's body:
- diffuse toxic goiter;
- nodular toxic goiter;
- inflammation of the thyroid gland with a subacute course;
- hormone-active tumors of the pituitary gland, accompanied by excessive synthesis of thyrotropin;
- pituitary form of resistance (resistance) to thyroid hormones;
- uncontrolled long-term treatment with synthetic thyroid drugs;
- ovarian tumors from embryonic cells called teratomas;
- excessive intake of iodine into the body;
- choriocarcinoma (malignant neoplasm from the chorionic villi - the embryonic part of the placenta);
- chronic liver damage;
- nephrotic syndrome.
These are the main etiological factors. Some increase in the average values of the hormone is observed in the first 14 weeks of physiological pregnancy.
When T4 free is below normal
The decrease in the content of thyroxine not associated with proteins in the blood serum occurs for the following reasons:
- weakening or cessation of the secretion of thyroliberin (a hormone that regulates the synthesis of TSH) in the hypothalamus (neoplasms, atrophic processes of the brain);
- insufficient production of TSH by the anterior lobe of the pituitary gland (traumatic brain injury, inflammatory processes, vascular disorders, tumors);
- inflammatory lesions of the thyroid gland (postpartum, autoimmune, specific, fibro-invasive, etc.);
- taking medications that suppress the synthesis of thyroid hormones;
- radiation exposure;
- dietary features leading to a lack of iodine in the body;
- resection or removal of the thyroid gland;
- dramatic weight loss in obese women.
Congenital disorders and abnormalities in the development of the gland, which do not allow it to function normally, also lead to a drop in thyroxine levels. As well as the neutralization of the hormone circulating in the blood, antibodies in autoimmune processes and proteolytic enzymes in severe inflammation of the pancreas, sepsis, shock.
The study of the free fraction of T4 helps in the determination of hypo- and hyperthyroidism
Tactics for deviation of T4 free from the norm
An increase and decrease in the level of the hormone leads to serious disturbances in metabolic processes in the body, because thyroid hormone receptors are present in almost all tissues.
Treatment with an increase in T4 free
When values go beyond the upper permissible limit, conservative and operational methods for correcting the level of active thyroxine are used. The choice of tactics is determined by the etiology of the disease leading to an increase in concentration.
The operation is indicated for hormone-producing pituitary adenoma, ovarian teratoma, choriocarcinoma. Resection and removal of the thyroid gland is rarely used and only in the absence of the effect of long-term conservative treatment. The use of radioactive iodine for therapeutic purposes is often avoided.
Drug stabilization of the hormonal background is achieved by using thyreostatic (suppressing the synthesis of thyroid hormones) drugs. Most often these are derivatives of methylmazole (Mercazolil, Methatilin, Methylmazol) and thiuracil (Propylthiouracil, Propicil). The therapy is carried out under strict laboratory control of the level of hormones in the blood.
Treatment with a decrease in free T4
Correcting low levels of free thyroxine also requires a differentiated approach. The main method is hormone replacement therapy. It is often lifelong. The exception is the conditions associated with the introduction of thyrostatic substances into the body.
For treatment, synthetic thyroid drugs (L-Thyroxin, Bagotyrox, Eutirox, etc.) are used. The effectiveness of the therapy is assessed by the presence and severity of clinical manifestations, the dynamics of laboratory parameters.
Conclusion
The concentration of the free T4 fraction in blood serum is an important criterion for assessing the state of the body. Therefore, it is advisable to determine the level of the hormone not only in the presence of the above complaints, but also during the women undergoing annual preventive examinations. This is especially true for patients over 40 years old. The delivery of such an analysis should become a mandatory procedure when planning a pregnancy.
Video
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Anna Kozlova Medical journalist About the author
Education: Rostov State Medical University, specialty "General Medicine".
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