T3 and T3 free: what is the difference between these indicators?

The article describes in detail two points of hormonal research - T3 and free T3, what is the difference between them, what is the relationship between these biologically active substances.

Here you can familiarize yourself with the analysis methodology and indications for it. The information is supplemented by an informative video in this article, as well as interesting photo materials.

Spatial and structural formulas of thyroid hormones

T3 hormone (triiodothyronine) is the most active of the main active substances produced by glandula thyreoide. The number “3” in the abbreviation means the presence of three iodine atoms in the molecule of the substance. This hormone is formed as a result of the breakdown of T4 (another active substance produced by the thyroid gland) in the process of splitting off one iodine atom from it.

Forms of existence of hormones

T3 exists in two forms, common and free. They are also indicated separately on the hormonal study form. So what is the difference between T3 general and T3 free?

The hormone produced in thyrocytes enters the blood, where most of it binds to protein molecules responsible for transporting the substance to the tissues that need it. However, a small amount of triiodothyronine circulates in the blood plasma without reacting with anything.

This is free T3. And the entire set of hormones, both associated with protein agents and those that have not reacted with them, is called total T3.

What tests to take to “check your thyroid gland”

Most often, an endocrinologist at an appointment assesses the condition using two indicators: TSH hormones and free T4.
There are receptors for the T4 hormone in the myocardium, and when an endocrinologist prescribes hormone replacement therapy for reduced thyroid function in the form of the synthetic hormone T4, sometimes signs of an overdose of T4 appear in the form of an increase in heart rate - tachycardia.

This is due to the reduced conversion of T4 to T3 - as I already said, T4 inside the cell must necessarily turn into the active hormone T3. Thus, a paradoxical situation arises: a patient may have signs of a hormone overdose and hypothyroidism at the same time.

Therefore, in my opinion, it is not enough to evaluate thyroid function solely by these two indicators. Although, according to medical and economic standards, a doctor in a free clinic is limited to precisely this volume of research.

If these indicators are normal, formally there are no problems with the thyroid gland. And they can be! Therefore, I always suggest that my patients undergo additional diagnostics.

Effect of triiodothyronine on the body

Regulation of mitochondrial function is one of the most important functions of T3

The task of this biologically active substance is to control the level of metabolism and energy.

Its action is multifaceted:

• absorption of carbohydrates;
• lipid breakdown;
• regulation of mitochondria;
• participation in the production of vitamin A;
• adjustment of mineral metabolism;
• stimulation of children's intellectual development;
• maintaining normal human body temperature;
• improving memory and performance in adults;
• increasing the passage of signals along nerve fibers;
• prevention of the development of atherosclerotic changes;
• synthesis of proteins, ribonucleic and deoxyribonucleic acids.

In addition, T3 regulates energy conversion and the transport of energy-rich compounds to those cells that need them.

How thyroid hormones are converted into each other

The thyroid gland produces iodothyronines (iodine-containing hormones) and is a “storage” of iodine in the body, and also participates in the synthesis of the hormone thyroxine (hereinafter T4) and triiodothyronine (hereinafter T3).

The production of T4 and T3 is regulated by the pituitary gland, which in turn releases TSH (thyroid stimulating hormone) if the amount of T4 and T3 is reduced. The pituitary gland is regulated by the hypothalamus, which produces thyrotropin-releasing hormone.

The formation of active T3 occurs from T4. But also from T4, under certain conditions, reverse T3 can be formed - this is a metabolically inactive isomer of the T3 hormone.

Here we must also say about the hormone leptin. This is such a “gray cardinal” of our body that can interfere with the work of other hormones. In particular, it affects adrenal and thyroid hormones.

Leptin can interfere with the effective functioning of the T3 hormone in this way: the more of it, the higher the rate of conversion of T4 into metabolically inactive reverse T3.

In this case, leptin has a regulatory effect on pituitary TSH. The mechanism of such influence in endocrinology is called “negative feedback”. How does it work?

The more hormones produced by the thyroid gland in the peripheral bloodstream, the less the need for TSH, which stimulates the production of these hormones. If there are not enough hormones, a signal is sent to the pituitary gland and thyroid-stimulating hormone levels increase to stimulate the thyroid gland to release more hormones.

And here’s what happens: if there is a lot of reverse T3, its regulatory effect on TSH remains, but the hormonal activity of reverse T3 is absent.

Thus, in a blood test, the TSH level turns out to be normal, taking into account the fact that the body perceived the total amount of T3 and T4 as sufficient. But in fact, active T3 is not enough. This will manifest as clinical signs of hypothyroidism.

If there is a malfunction of the thyroid gland, as a result, metabolic processes occurring every second in the body are disrupted. The thyroid gland also produces the hormone calcitonin, an important hormone for the skeletal system, which is involved in the restoration of bones and prevents their destruction.

When the functions of the thyroid gland are increased, the metabolic rate increases, and vice versa, if it is sluggish, the metabolism slows down.

Standards for the content of various forms of T3

The highest T3 content is observed in children from the 4th day to the 12th month of life

Depending on the gender and age of a healthy person, his blood contains free T3 and total T3 in concentrations from 1.30 to 7.50 nmol/liter. The concentrations of these substances, taking into account age, are given in the following tables.

Triiodothyronine (total):

Important! Only a specialist can interpret the results of the study. Self-diagnosis in the case of hormonal levels is strictly prohibited.

On average, women's results are 5 to 10 percent lower than men's. Pregnancy leads to an even greater decrease in the content of total triiodothyronine, and its restoration occurs no earlier than 7 days after the birth of the child. A further decrease in hormone levels is observed in both sexes upon reaching the age of sixty-five.

Starting at age 65, T3 levels begin to decline noticeably

Triiodothyronine (free):

In order to obtain correct results, the influence of a number of factors must be excluded.

After all, indicators can change significantly under the influence of:

• stress;
• physical activity;
• sports training;
• consumption of alcoholic beverages and drugs;
• changes in the seasons of the year (maximum values ​​in autumn and winter, and minimum values ​​in summer);
• errors in the diet that must be followed on the eve of collecting biological material;
• taking medications such as hormones (including contraceptives), salicylates, amiodarone, coumarin (and derivatives), drugs containing iodine and lithium.

Different laboratories may use different systems for determining T3 levels

Important! When taking an analysis for T3, it should be taken into account that each laboratory may have its own internal instructions for carrying out the procedure, since the study can be carried out using several different algorithms and the results, accordingly, may differ and be indicated in different units of measurement.

As a rule, on the forms of each laboratory there is a table of normal, reference values ​​of the indicator for ease of comparison and interpretation of the result by the specialists who ordered the study.

What factors affect triiodothyronine levels?

The T3 hormone, the norm in women is lower than in men, can change its concentration under the following conditions:

• Age. In children, the amount of biologically active substances in the thyroid gland reaches the level of adults by the age of 11-15 years. With age (after 65 years), its concentration gradually decreases.
• During pregnancy, the physiological norm is a slight decrease in the amount of this hormone, which is restored after childbirth.
• Seasonal changes. After taking a test for triiodothyronine in winter, the norm in women and men may be increased. Conversely, during the summer months there is an increase in thyroid hormone levels.

What common

As is clear from the above, both total and free triiodothyronine are one substance. The difference in these indicators and the relationship of one of them to the other can tell a specialist a lot about the condition of not only the thyroid gland, but also many other organs of the body. Based on this knowledge, you can request other tests or make a specific diagnosis for the patient.

In order to calculate both important indicators based on T3 levels, doctors resort to analyzing the composition of venous blood. Before taking a test, the patient must meet a number of requirements:

• Avoid taking iodine-containing medications, oral contraceptives and other hormonal drugs at least 14 days before the test;
• 2 days before the test, completely stop smoking and drinking alcohol;
• a day before, refrain from eating fatty, spicy, smoked and salty foods, as well as tonic drinks;
• also limit heavy physical activity during the day and eliminate the strong influence of stress factors;
• 12 hours before the test, stop taking any food and nicotine substitutes.

Only by complying with all the requirements can you obtain a “clean” analysis that indicates the real content of T3 in the body.

T3 increased

The T3 level increases, as a rule, against the background of hyperfunction of the glandula thyreoide. This occurs in parallel with an increase in T4 production, but with T3 thyrotoxicosis, the thyroxine content may remain within normal limits.

An increase in triiodothyronine content leads to the appearance of specific symptoms:

• diarrhea;
• insomnia;
• hypertension;
• tachycardia;
• fussiness;
• photophobia;
• anxiety;
• trembling hands;
• heartbeat;
• tearfulness;
• rapid weight loss;
• sudden aggression;
• nervous excitability;
• feeling of “sand in the eyes”;
• frequent urge to urinate;
• enlargement of the mammary glands in men;
• hyperthermia, in the absence of cold symptoms;
• irritability, turning into lethargy and further into apathy;
• menstrual cycle disorders in women - disruptions, heavy bleeding, severe pain.

Gynecomastia is one of the signs of increased triiodothyronine levels

An increase in triiodothyronine concentration may be a symptom of the following diseases:

• Thyrotrypinoma is a benign tumor of the pituitary gland, which, through increased secretion of thyrotropin, stimulates increased production of T3 hormone.
• Toxic goiter. In this case, the doctor diagnoses an increase in the size of the gland, increased heart rate and protrusion of the eyeballs.
• Isolated T3 toxicosis.
• Thyroiditis, which is an inflammatory lesion of the organ.
• Thyrotoxic adenoma is a benign neoplasm of the thyroid gland that causes hypersecretion of hormones.
• Postpartum dysfunction of the endocrine system.
• Choriocarcinoma is a malignant tumor that forms from germinal tissues during pregnancy.
• Hemodialysis. Instructions for artificial cleansing of the circulatory system indicate a possible increase in hormonal levels.
• Chronic liver and kidney diseases.

Tactics for increasing T3 content

For further examination and treatment, you should contact an endocrinologist. The doctor will decide on treatment tactics; as a temporary measure, thyreostatics will most likely be prescribed - substances that suppress or block the production of thyroid hormones. The price of treatment depends on many factors, but the earlier the fight against pathology begins, the lower it is.

How is the examination carried out?

The study requires standard venous blood sampling.

The procedure is carried out in the manipulation room with the patient in a sitting position. The arm is exposed to the level above the elbow, a special tourniquet is applied to it, which slows down the outflow of blood from the limb itself. The future injection site is disinfected twice: first along a larger radius, later more centrally.

After this, a needle is inserted into the vein at an acute angle. If a regular syringe is used during the procedure, the nurse makes a test to see if it gets into the vessel by pulling the piston towards herself. The appearance of blood will mean that the needle is in a vein.

If modern vacuum tubes are used, a small amount of blood enters the indicator chamber of a disposable needle on its own, which also indicates that it has entered the vessel. The tube is attached to the needle and filled with blood. This test tube must be labeled. This is followed by removing the needle from the vein and clamping the vein with a swab containing an alcohol solution or another antiseptic.

This procedure is routine and the risks of any complications are minimal. Emotionally unstable patients may experience dizziness and short-term loss of consciousness. Loss of consciousness can also occur in people with low blood pressure. It is extremely rare that people with blood clotting disorders may experience prolonged bleeding from the injection site.

T3 decreased

The decrease in triiodothyronine content occurs solely against the background of a decrease in the production of all other thyroid hormones.

This phenomenon is observed in several serious pathologies:

• hypothyroidism;
• endemic goiter;
• Hashimoto's thyroiditis;
• treatment with radioactive iodine;
• resection of part of the glandula thyreoide or the entire gland with a cavity;
• taking certain medications containing large amounts of iodine, such as cordarone and others.

The drug "Cordarone" can provoke a decrease in thyroid hormone levels

It should be noted that the drop in thyroid hormone levels does not occur chaotically. At first, there is always a decrease in T4 content, and then in triiodothyronine. There is a reason for this.

The activity of T3 is ten times higher than that of T4, therefore, with an acute need for T3, the mechanism of peripheral conversion of thyroxine to triiodothyronine is triggered. And only after T4 reserves are depleted, T3 begins to noticeably decrease.

If, nevertheless, T3, T4 total or free dropped significantly, symptoms of hypothyroidism begin to develop, manifested by:

• swelling;
• nausea;
• constipation;
• chilliness;
• hypotension;
• hypothermia;
• drowsiness;
• puffiness;
• general weakness;
• decrease in speech quality;
• increase in body weight;
• dry skin;
• decreased activity of thinking;
• menstrual cycle disorders;
• depression coupled with irritability;
• decreased potency, up to impotence;
• myxedema (in severe forms of pathology in adults);
• cretinism (with severe disease in children).

Impotence may also be based on a decrease in T3 levels

Also, the reasons why free T3 or total T3 decreases can be pathologies of the pituitary gland, such as hypopituitarism, empty sella syndrome, and others.

Tactics for reducing T3

Most often, treatment begins with the prescription of replacement therapy, synthetic analogues of thyroid hormones. But, in any case, if the T3 level decreases, self-medication is strictly prohibited; you should immediately seek advice from an endocrinologist.

Antibodies to thyroid peroxidase (AT-TPO, microsomal antibodies)

Autoantibodies to the enzyme of thyroid cells.

Antibodies to thyroid peroxidase are an indicator of the aggression of the immune system towards its own body. Thyroid peroxidase provides the formation of an active form of iodine, which can be included in the process of iodification of thyroglobulin. Antibodies to the enzyme block its activity, as a result of which the secretion of thyroid hormones (T4, T3) decreases. However, TPO Abs can only be “witnesses” of the autoimmune process.

Thyroid peroxidase antibodies are the most sensitive test for detecting autoimmune thyroid disease. Usually their appearance is the first shift that is observed in the course of developing hypothyroidism due to Hashimoto's thyroiditis. When sufficiently sensitive methods are used, TPO Abs are detected in 95% of people with Hashimoto's thyroiditis and in approximately 85% of patients with Graves' disease. Detection of AT-TPO during pregnancy indicates the risk of developing postpartum thyroiditis in the mother and a possible impact on the development of the child.

Reference limits largely depend on the research method used. Low levels of AT-TPO can sometimes be found in apparently healthy people. It remains unclear whether this may reflect a physiological norm, or is a precursor to autoimmune thyroiditis, or is a problem with the specificity of the method.

Limits of determination:

3 U/ml - 1000.0 U/ml.

T3 and pregnancy

During pregnancy, the concentration of triiodothyronine can go beyond normal limits, but this does not indicate the onset of the disease. In the first trimester, this is even considered as a variant of the norm, especially since in the second trimester, T3 free and total, the difference between the contents of which in this case does not matter much, return to previous indicators.

If the concentration of the hormone drops, then in this case doctors will take emergency measures and prescribe the pregnant woman hormone replacement therapy with synthetic analogues of triiodothyronine. This should be done as quickly as possible so that the fetus does not suffer due to an acute lack of T3.

Fetal development may go wrong if the level of T3 hormone in the blood decreases

An accurate determination of the total triiodothyronine content during pregnancy is difficult, since in this state the test subject’s body intensively synthesizes proteins, some of which bind the hormone, resulting in an increased result. This will do nothing but add extra stress to the pregnant woman.

And for accurate diagnosis, the level of free T3 is used. Therefore, for pregnant women, the question of whether T3 is common or free, which one to take, can be answered that preference should still be given to the free one.

Why is a T3 hormone test necessary?

To determine the condition of the thyroid gland, the endocrinologist must give the patient a referral for blood tests for three hormones - TSH, T4, T3. Testing for triiodothyronine is considered very important, as it allows to minimize diagnostic error.

For example, quite often working nodes in nodular toxic goiter reproduce the hormone T3. Its amount can also increase in diseases such as diffuse toxic goiter and Graves' disease. If the test result shows a significant increase in the amount of triiodothyronine, then doctors diagnose T3 toxicosis. This condition is quite difficult to treat with medications.

How to support the thyroid gland with nutrition?

Adequate functioning of the thyroid gland is facilitated by a huge number of cofactors - “helper molecules” that participate in biochemical transformations. In particular, these include iron (a laboratory indicator of tissue iron reserve is ferritin) and selenium - an important element that prevents the occurrence of an autoimmune condition. Of course, zinc and copper are important.

Therefore, I recommend including foods rich in these microelements in your diet. For example, 2-3 Brazil nuts contain your daily dose of selenium. Seafood contains a lot of zinc, and offal contains iron. Moreover, these products must be whole, and not processed into semi-finished products.

Whole foods are associated with the concept of nutritional density, also known as specific calorie content. This is the amount of microelements, vitamins and macroelements, as well as proteins, fats and carbohydrates, which account for 1 kcal. The more of these substances there are per 1 kcal, the more nutritious the product is considered and the more preferable it is for inclusion in the human diet.