Instructions for use L-THYROXIN 100 BERLIN-CHEMIE (L-THYROXIN 100 BERLIN-CHEMIE)

52139 06 August

IMPORTANT!

The information in this section cannot be used for self-diagnosis and self-treatment.
In case of pain or other exacerbation of the disease, diagnostic tests should be prescribed only by the attending physician. To make a diagnosis and properly prescribe treatment, you should contact your doctor. We remind you that independent interpretation of the results is unacceptable, the information below is for reference only
T4 free, Free Thyroxine, FT4:
indications for use, rules for preparing for the test, interpretation of the results and normal indicators.

Indications for prescribing the study

Free thyroxine (T4 free, Free Thyroxine, FT4) is a fraction of the main thyroid hormone, thyroxine (T4), not bound to proteins.
The study is aimed at assessing thyroid function. The test is carried out:

• with clinical signs of increased or decreased activity of the thyroid gland;
• with an increase in the size of the thyroid gland (goiter);
• with a previously identified change in the level of thyroid-stimulating hormone;
• to monitor treatment for established thyroid diseases.

No. 55 Laboratory assessment of thyroid function

Free thyroxine (Free Thyroxine, FT4) In this study, the concentration of the free fraction of thyroxine, the dominant thyroid hormone, is determined in the blood serum. This study is advisable to carry out in the presence of signs of hypothyroidism or thyrotoxicosis, with a decreased or increased level of TSH, as well as with identified diffuse toxic goiter.

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Signs of decreased and increased thyroid hormone levels

When the production of thyroid hormones is low, hypothyroidism develops. The disease can occur for a long time without significant symptoms.

The main manifestations of low levels of thyroid hormones:

• decreased performance;
• the appearance of daytime drowsiness and some inhibition of reactions;
• frequent illnesses due to weakened immune defenses;
• swelling in the legs and arms;
• disruption of the female menstrual cycle;
• instability to low temperatures and increased sensitivity to cold;
• deterioration of skin and hair condition.

When the concentration of thyroid hormones increases, the following signs appear:

• weight loss;
• cardiopalmus;
• unstable mental state;
• trembling of fingers;
• increased sweating;
• formation of a goiter in the neck area;
• physical weakness and high fatigue.

Preparation for the procedure

1. Blood should be donated for testing at the same time (if it is necessary to track the dynamics of the indicator or the effectiveness of treatment), preferably between 8:00 and 12:00.
2. Discuss with your doctor the use of medications that affect the level of thyroid hormones (hormone replacement therapy, thyreostatic drugs). To assess the function of the thyroid gland, it is necessary, in agreement with the doctor, to cancel them a month before the test.
3. Two to three days before the test, avoid physical activity, sports training, and stress.
4. On the eve of the analysis, it is not recommended to conduct studies using radiocontrast agents.

Side effects of the drug L-thyroxine Berlin-Chemie

When using the drug, tachycardia, increased heart rate, arrhythmia, angina pectoris, tremor, a feeling of internal restlessness, insomnia, hyperhidrosis, a feeling of heat, increased body temperature, weight loss, vomiting, diarrhea, headache, weakness and muscle spasms, menstrual irregularities may occur. . If these symptoms appear, it is recommended to reduce the daily dose or interrupt the drug for several days. As soon as the side effects disappear, you can return to treatment again, carefully increasing the dosage of the drug. Allergic reactions may occur in the form of urticaria, bronchospasm and laryngeal edema, and in some cases, anaphylactic shock.

What can affect the result

1. Taking medications: iodine, thyroid hormones, thyreostatics (drugs that reduce the production of thyroid hormones), oral contraceptives (birth control pills), anabolic steroids, glucocorticosteroids, antibiotics, heparin, anticonvulsants, propranolol (a beta-blocker drug), diuretics (diuretics), etc.
2. Recent thyroid surgery, radiotherapy.
3. Increased body weight.
4. Time to apply a tourniquet when drawing blood.
5. Time of blood donation: the highest level of free thyroxine is recorded from 8:00 to 12:00, the lowest - from 20:00 to 03:00.
6. Time of year: the level of free thyroxine in the autumn-winter period is lower than in summer.
7. Pregnancy (free thyroxine levels fluctuate).

You can donate blood for free T4 at the nearest INVITRO medical office.
A list of offices where biomaterial is accepted for laboratory research is presented in the “Addresses” section. Interpretation of study results contains information for the attending physician and is not a diagnosis.
The information in this section should not be used for self-diagnosis or self-treatment. An accurate diagnosis is made by the doctor, using both the results of this examination and the necessary information from other sources: medical history, results of other examinations, etc. The thyroid gland is the largest gland of the endocrine system.

It accumulates iodine and produces iodine-containing hormones - thyroxine (tetraiodothyronine, T4) and triiodothyronine (T3). The synthesis of these hormones requires thyroglobulin (TG), a precursor to T4 and T3, the only source of which is the thyroid gland, but whose secretion is controlled by thyroid-stimulating hormone (TSH). TSH, in turn, is synthesized by the pituitary gland (pituitary gland), which is located at the base of the brain. The main function of the pituitary gland is to maintain a constant concentration of thyroid hormones.

Thyroid hormones are found in the blood both in free form and bound to special carrier proteins. Only free forms of hormones exhibit biological activity. Thyroxine (T4) is one of the two main thyroid hormones.

Thyroxine secretion is regulated by a feedback system that the body uses to maintain stable levels of thyroid hormones in the blood.

If the level of thyroid hormones in the blood decreases, the pituitary gland begins to produce more thyroid-stimulating hormone (TSH), which stimulates the thyroid gland, and the secretion of T4 and T3 increases.

If the level of T3 and T4 in the blood, on the contrary, increases, then the pituitary gland reduces the secretion of TSH, and the thyroid gland, in turn, produces less T4 and T3.

If the thyroid gland does not produce enough T4 and T3 due to thyroid dysfunction or insufficient TSH levels, a person will experience symptoms of hypothyroidism: weight gain, dry skin, cold intolerance, irregular periods and fatigue.

If the thyroid gland produces too much T4 and T3, a person may experience symptoms associated with hyperthyroidism: rapid heart rate, anxiety, weight loss, trouble sleeping, tremors in the hands, and dry, irritated eyes. In some cases, exophthalmos (bulging eyes) is a characteristic symptom.

Functions of thyroid hormones

Thyroid hormones have a huge impact on almost all organs and systems of the human body. Their effects largely depend on concentration. For example, in small quantities, thyroid hormones have an anabolic effect and help increase protein synthesis and inhibit muscle destruction. A high concentration of thyroid hormones, on the contrary, leads to catabolic breakdown and maintenance of a negative nitrogen balance.

The main functions of thyroid hormones:

• stimulation of tissue growth and development;
• support for mental and physical health, speed of thought processes;
• participation in all types of metabolism;
• maintaining optimal blood glucose levels;
• influence on glycogen synthesis and muscle tissue;
• increased lipolysis, prevention of active fat deposition in problem areas of the body;
• strengthening of hematopoietic processes in the bone marrow;
• maintaining optimal cholesterol levels in the blood.

T3 general and T3 free

The biological role of T3 is higher than T4. Some triiodothyronine is produced in the thyroid gland, but most is synthesized in the process of obtaining thyroxine from the external environment.

1. General T3 stimulates bone growth and the production of certain sex hormones. In children, this substance is responsible for the growth and formation of the central nervous system. Total T3 can affect cholesterol levels and the rate of protein metabolism.
2. Free T3 controls all types of metabolism, the functioning of the heart, respiratory, reproductive, and digestive systems.

T4 general and T4 free

1. T4 general is responsible for obtaining energy and maintaining the tone of the nervous system. The hormone is predominantly in a protein-bound state.
2. Free T4 is the active part of thyroxine. The hormone is in the bloodstream in a state not bound to proteins. Free T4 regulates metabolic processes, increases oxygen consumption by tissues and produces heat. It also helps prevent atherosclerosis by preventing the formation of cholesterol plaques on the walls of blood vessels. Free T4 controls and increases the functionality of the reproductive system, respiratory organs, is responsible for a calm and even mood, the stability of a person’s mental state.

Interpretation of results in children and adults

The main reasons for the increase in the concentration of free thyroxine

1. Hyperfunction of the thyroid gland with:

• diffuse toxic goiter. The development of the disease is preceded by disturbances in the activity of the thyroid gland of genetic, autoimmune or inflammatory origin. Unfavorable factors (stress, respiratory infections) can activate the thyroid gland and provoke the development of the disease;
• thyroiditis – inflammation of the thyroid gland of an infectious or autoimmune nature;
• postpartum thyroiditis. The pathology is considered a variant of autoimmune thyroiditis. The classic manifestation is temporary thyrotoxicosis, which occurs in three phases (thyrotoxicosis, hypothyroidism, recovery).

1. Taking synthetic thyroid hormones.
2. Excessive intake of iodine into the body (including with radiocontrast agents).
3. Pathologies affecting the level and ability of specific proteins to bind hormones (hepatitis and cirrhosis lead to a decrease in the level of thyroxine-binding globulin).
4. Tumors of the pituitary gland, accompanied by an increase in the level of thyroid-stimulating hormone.

The main reasons for the decrease in the concentration of free thyroxine

1. Weakening of thyroid function in primary hypothyroidism, after removal of a lobe of the thyroid gland, and in case of thyroid cancer.
2. Taking thyreostatic drugs.
3. Iodine deficiency.
4. Secondary hypothyroidism, in which the pituitary gland produces little thyroid-stimulating hormone. Causes: inflammation or neoplasm in the pituitary gland.
5. Tertiary hypothyroidism, caused by a decrease in the production of thyrotropin-releasing hormone by the hypothalamus due to traumatic brain injury, inflammatory, autoimmune, and vascular disorders.

If the indicator deviates from the norm, the following studies are additionally carried out: total triiodothyronine (T3 total, Total Triiodthyronine, TT3), free triiodothyronine (T3 free, Free Triiodthyronine, FT3), total thyroxine (T4 total, total tetraiodothyronine, Total Thyroxine, TT4), thyroid stimulating hormone (TSH, thyrotropin, Thyroid Stimulating Hormone, TSH).

Interactions of the drug L-thyroxine Berlin-Chemie

In the case of combined use of levothyroxine with cholestyramine or colestipol, an interval of 4–5 hours should be maintained between their doses (cholestyramine/colestipol inhibits the absorption of levothyroxine). The absorption of levothyroxine may be reduced by concomitant use of aluminum-containing antacids, calcium carbonate or iron-containing drugs, so it should be taken at least 2 hours before taking these drugs. Propylthiouracil, corticosteroids, β-adrenergic receptor blockers and iodine-containing contrast agents inhibit the conversion of T4 to T3. Amiodarone, due to its high iodine content, can cause both hypothyroidism and hyperthyroidism. Particular care should be taken in case of nodular goiter with the possibility of unrecognized autonomy. Rapid intravenous administration of phenytoin can lead to an increase in the plasma concentration of free levothyroxine, liothyronine and, in some cases, provoke the appearance of cardiac arrhythmias. Under the influence of furosemide in high (250 mg) doses, as well as salicylates, dicumarol, clofibrate, levothyroxine may be displaced from the sites of its binding to blood plasma proteins and, as a result, its action may be enhanced. Sertraline and chloroquine/proguanil reduce the effectiveness of levothyroxine and increase serum TSH levels. During the use of contraceptives containing estrogens or during postmenopausal hormone therapy, the need for levothyroxine may increase. Products containing soy may reduce the intestinal absorption of levothyroxine, which may require dose adjustment. Under the influence of levothyroxine, a decrease in the hypoglycemic effect of insulin and oral antidiabetic drugs may occur. For this reason, in patients with diabetes mellitus using levothyroxine, regular monitoring of blood sugar levels is necessary (especially at the beginning of therapy), and, if necessary, dosage adjustment of antidiabetic drugs. Levothyroxine may enhance the effect of coumarin derivatives, therefore, when used simultaneously, regular monitoring of blood clotting is necessary, and, if necessary, dose adjustment of the anticoagulant drug.

Overdose of the drug L-thyroxine Berlin-Chemie

In case of overdose, an accelerated pulse, increased heartbeat, sweating, arrhythmia, insomnia, tremor, increased frequency of angina attacks, and worsening of diabetes mellitus are noted. It is recommended to stop taking the pills and conduct follow-up examinations. If severe tachycardia develops, it can be weakened with the help of β-adrenergic receptor blockers; thyreostatic agents are not used. When taking levothyroxine in a very high dose (suicide attempt), plasmaphoresis is used.

Comprehensive analysis, including determination of the level of free T3, free T4 and reverse T3 (rT3). In combination with other indicators, the study allows you to assess the functional state of the thyroid gland.

Composition of the study:

• Thyroxine (T4) free
• Triiodothyronine (T3) free
• Triiodothyronine reverse (rT3)

English synonyms

T4 (Thyroxine), T3 (Triiodothyronine), T3 (Triiodothyronine) Reverse, Serum.

Research method

High performance liquid chromatography.

Units

Pg/ml (picograms per milliliter).

What biomaterial can be used for research?

Venous blood.

How to properly prepare for research?

• Children under 1 year of age should not eat for 30-40 minutes before the test.
• Do not eat for 2-3 hours before the test; you can drink clean still water.
• Avoid (in consultation with your doctor) taking steroid and thyroid hormones for 48 hours before the test.
• Avoid physical and emotional stress for 24 hours before the test.
• Do not smoke for 3 hours before the test.

General information about the study

Iodine-containing hormones - thyroxine and triiodothyronine - in the human body are produced in the cells of the follicular epithelium of the thyroid gland, located in the thickness of the anterior tissue of the neck. For the formation of thyroid hormones, iodine atoms are necessary: ​​the thyroxine molecule contains four of them, and therefore the second name of this hormone is T4, and the triiodothyronine molecule contains three, respectively, T3. In the peripheral blood, more than 99% of thyroid hormones circulate in a state bound to plasma proteins. Since hormone receptors are located inside cells, and plasma proteins are too large and cannot penetrate into the cell through its membrane, the T4 and T3 associated with them do not have metabolic activity. A small amount (0.03% thyroxine and 0.3% triiodothyronine) circulates in the blood without binding to plasma proteins and constitutes the free fraction of thyroid hormones, which is metabolically active. The total amount of T3 and T4 is, respectively, the sum of their bound and free fractions.

The thyroid gland produces approximately ten times more T4 than T3. However, despite the fact that thyroxine is the main product of its secretory activity, it is not the most active agent; triiodothyronine is a more powerful hormone. Unlike thyroxine, the entire circulating pool of which is formed in the thyroid gland, only 20% of T3 is of thyroid origin. The rest is formed in the cells of peripheral tissues by enzymatic transformation from T4: under the influence of enzymes of the deiodinase class, one of the four iodine atoms included in its composition is split off from the thyroxine molecule. Depending on the position in the structure of the thyroxine molecule from which the iodine atom is split off, either T3 or reverse triiodothyronine (rT3) is formed. Currently, three types of deiodinases are known: D1, D2 and D3. D1 and D2 are responsible for the conversion of T4 to T3, and D3 promotes the formation of reverse T3 from T4. D3 is found predominantly in cells of the central nervous system, skin, hemangiomas, fetal tissue and placenta. Reverse T3 is the third major form of thyroid hormone circulating in the blood. At the level of molecular structure, T3 and rT3 are almost mirror images of each other, however, there are significant differences in their biological function. Reverse T3 has no biological activity, but it can bind to the same receptors as T3, blocking the latter's interaction with them. The formation of reverse T3 is an additional physiological mechanism for protecting the body from excess T3. In severe illnesses and prolonged fasting, when a decrease in metabolism is justified in order to maintain homeostasis of the body, the conversion of T4 to T3 decreases, and T4 to rT3, on the contrary, increases. This reflects adaptive metabolic capabilities that help protect tissues from the catabolic effects of thyroid hormones.

Thus, the ratio of the levels of thyroxine and its metabolites partly reflects the functional state of the thyroid gland and the processes of thyroid hormone metabolism. The concentration of T4, T3 and reverse T3 is studied by liquid chromatography with tandem mass spectrometry. This high-tech research method is based on the ability to separate mixtures of substances into structurally identical individual components, followed by counting their quantities.

What is the research used for?

• To assess the metabolism of thyroid hormones, including at the level of peripheral tissues.

When is the study scheduled?

• If you suspect the development of a condition caused by a decrease in the formation of triiodothyronine in peripheral tissues, for the purpose of differential diagnosis with thyroid pathology (hypothyroidism).

What do the results mean?

Reference values, pg/ml

Testing the level of reverse T3 is considered appropriate in a small number of clinical situations. Determination of the rT3 level is of primary importance in the differential diagnosis of hypothyroidism and the so-called Euthyroid sick syndrome - a state of dysregulation of control over the synthesis of thyroid hormones, which occurs against the background of prolonged fasting and severe illness, in the absence of thyroid pathology. Laboratory tests for this syndrome often reveal a decrease in T3, a decrease or normal level of T4, and a normal level of thyroid-stimulating hormone. Pathogenetically, the decrease in T3 levels in this situation is due to an increase in the activity of D3 deiodinase, which leads to increased synthesis of reverse T3 from thyroxine. Accordingly, the concentration of rT3 will increase, and the level of T3, on the contrary, will decrease. This helps differentiate Euthyroid sick syndrome from hypothyroidism and refrain from prescribing levothyroxine replacement therapy.

Another indication for rT3 testing is in the evaluation of patients with massive hemangiomas . The cells of this benign tumor are capable of producing large amounts of deiodinase D3, which promotes the formation of reverse T3 from thyroxine and the development of a hypothyroid state.

In addition, an increase in rT3 levels is observed in healthy newborns, in patients with hyperthyroidism, and also when taking certain medications (amiodarone, propranolol).

What can influence the result?

• Taking certain medications: amiodarone reduces T3 levels, phenytoin (an antiepileptic drug), salicylates (including acetylsalicylic acid) lead to the release of T3 from serum proteins.