Interpretation of the results of a blood test for thyroid hormones. T3 - thyroid hormone: what it is responsible for, the norm and deviations from the norm What is affected by low and high levels of T4

The thyroid gland performs one of the main functions in the body; it produces hormones that are extremely important for normal human functioning. One of these hormones is free T3 (triiodothyronine). The number three in the abbreviation indicates the number of iodine atoms contained in its molecule. It is formed by follicular cells as a result of the cleavage of one iodine atom from thyroxine (T4).

The main role of free T3 is to stimulate tissues to absorb oxygen and activate metabolic function. In total, the associated hormone T3 forms the total T3 index. However, free T3 hormone is considered a more reliable indicator, with the exception of intensive care patients. In this case, reliability will be obtained by performing blood tests for total T3 content.

Free T3 is the active link of total T3. Its increased concentration in blood atoms does not affect the decrease in the amount of protein, because it is freely moving and does not interact with the carrier protein.

Produced by follicular cells and released into the bloodstream. When it enters the bloodstream, it begins to interact with protein molecules that facilitate its movement to sites where oxygen is absorbed.

You can find out what the hormone is responsible for from the list of its functions below:

accelerates the absorption of oxygen by tissues, except for the cellular tissues of the brain and glands of the genital organs;
increases heat generation in the human body;
promotes intensive protein metabolism in blood cells;
increases the accumulation of glucose in the blood;
lowers the concentration of cholesterol and triglycerides;
stimulates the production of vitamin A in the liver;
stimulates the removal of calcium from the blood
stimulates contractions of the heart muscles;
forms alveoli in infants;
enhances the wave-like contraction of the intestinal walls, promoting normal excretion of contents;
increases the formation of red blood cells;
controls metabolism in bone tissue;
enhances the function of removing harmful substances and medications from the blood.

Referrals for tests are usually given to identify the level of concentration of free T3, since it is its normal concentration in the blood that is of particular importance for the functioning of the entire body. The indicator determines the pathology of the thyroid gland.

Hormone analysis

First of all, the endocrinologist gives the patient a direction to test for hormones T3, T4, TSH. These are the main studies in determining disorders in the thyroid gland. Often, in order to save one’s own budget, a blood test for free T3 content is not carried out; however, this is the wrong decision, which leads to an error in the diagnosis.

Note that in case of nodular toxic goiter, the thyroid nodes working together produce precisely free triiodothyronine. The disease passes with clearly identified signs and is very slowly eliminated with drug therapy. Also, an increased level of the hormone indicates diseases such as Graves' disease or diffuse toxic goiter. If the T3 hormone is St. significantly exceeded the limit, doctors diagnose T3 toxicosis.

The level of hormone concentration is determined by blood from a vein. The exact value can be obtained if you follow important rules:

the patient must donate blood on an empty stomach, otherwise the indicator will not be reliable;
one month before the procedure, all medications containing thyroid hormones are discontinued;
five days before the study, the patient must exclude all physical activity;
The last time you are allowed to eat is 8 hours before the test.

In general, decoding analyzes is a rather complex process, since the result depends on the equipment on which the analysis is carried out. The norm is determined according to the data indicated on the laboratory form, which is printed from a computer program. If the hormone indicators are written by hand, it is considered that the analysis was carried out incorrectly, without the appropriate reagents or equipment.

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As the form data shows, the normal level of the hormone must fall within certain threshold values, this is from 2.6 to 5.7 pmol/l.

The normal concentration of the hormone in a child has a number of differences from that of an adult. For example, before adolescence, indicators are distributed separately for boys and separately for girls. In the table below you can see the limits of values by age and gender of the child:

Increased level

When free T3 hormone is elevated, the patient experiences:

increased sweating;
the skin becomes warm and moist to the touch;
hair becomes thinner;
increased contraction of the heart muscles;
abnormal heartbeat (arrhythmia);
increased appetite;
increased wave-like contraction of the intestinal muscles, a tendency to diarrhea appears;
increased systolic blood pressure;
sudden weight loss;
the appearance of nervousness, emotional instability;
muscle weakness;
fast fatiguability;
hand trembling;
widening of the palpebral fissures, protrusion of the eyeballs;
the calcium content in blood cells increases;
Irregularity of menstruation.

All of the above symptoms mean that their manifestation indicates the presence of a number of diseases, such as toxic goiter, adenoma, meloma, chronic pathological processes in the liver, nephrotic syndrome, thyrotropinoma, thyroid dysfunction in the postpartum period.

An increased level of free T3 also manifests itself in cases of excessive thyroid function (thyrotoxicosis) and iodine deficiency. Or with long-term use of medications that directly affect the level of hormones (oral contraceptives, estrogens, etc.).

Reduced level

If a patient's free T3 hormone level is low, the following symptoms are observed:

hair loss;
weakness of the eyelids;
decreased field of vision;
loss of appetite;
weakened intestinal motility, frequent constipation;
inhibition of actions;
muscle weakness;
decreased contraction of the heart muscles;
impotence (in men);
frequent with heavy menstruation (in women);
increase in cholesterol levels.

The listed disorders reflect a decreased level of the hormone, which indicates the presence of diseases such as primary hypothyroidism of congenital origin (underdevelopment or complete absence of the thyroid gland), acute iodine deficiency, acute thyroiditis, severe pathology of internal organs, chronic liver disease, protein deficiency .

Note that a low hormone level does not always indicate the presence of various diseases. There is a decrease in its concentration in expectant mothers in the third trimester of pregnancy. As a rule, with the birth of the baby the indicator returns to normal.

Having determined the results of the analysis, you should not make hasty conclusions and make a diagnosis yourself, relying only on the free T3 indicator. Often, for accurate diagnosis, it is necessary to check the status of hormone concentrations in the body as a whole. It is also important to say that drug therapy is prescribed only by the attending physician, having assessed test data, performed an examination and determined the individuality of the body.

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Today, very often, to diagnose a wide variety of diseases, a blood test is prescribed for hormones produced by the thyroid gland. This study consists of determining the level of thyroid hormones (thyroxine and triiodothyronine - T4 and T3, respectively), which are produced by the thyroid gland, as well as the associated thyroid-stimulating hormone (TSH), produced by the pituitary gland. The analysis allows the endocrinologist to assess the condition of an important organ of the human body as a whole and correctly prescribe treatment if a deviation from the norm is detected.

Characteristics of hormones

Thyroid-stimulating hormone is produced in the pituitary gland, which is located at the base of the brain. Its functional purpose is to stimulate the production of hormones by the thyroid gland:

T3 (triiodothyronine),
T4 (thyroxine).

Triiodothyronine and thyroxine are very important highly active biological substances responsible for general human health. T3 and T4 ensure proper metabolism, normal functioning of the autonomic, cardiovascular and digestive systems, and also support the mental functions of the human body. Thyroid-stimulating hormone, triiodothyronine and thyroxine are interdependent. On the one hand, TSH stimulates the production of T3 and T4 by the thyroid gland, and when their levels rise, these substances suppress the production of TSH in the pituitary gland. Thus, in a healthy human body, self-regulation of hormonal balance occurs, based on “feedback”.

The condition in which T3 and T4 are produced in normal quantities is called eutheriosis. In endocrinology, the following pathologies are distinguished when the norm is violated:

Hypothyroidism - with a deviation in the direction of decrease.
Hyperthyroidism - with a deviation in the direction of increase.
Thyrotoxicosis - with active production of biological substances.

TSH norm

An important indicative test is the determination of TSH in the blood. Such a study is prescribed simultaneously with tests for T3 and T4 produced by the thyroid gland. The TSH norm varies depending on age and can be in honey/l:

for newborns – 0.7–11;
for children over 10 weeks – 0.6–10;
up to two years – 0.5–7;
up to five years – 0.4–6;
up to 14 years – 0.4–5;
for adults – 0.3–4.

The largest amount of TSH in healthy people is detected in the morning. If the level is significantly higher than normal, this means that the thyroid gland produces an insufficient amount of thyroid-stimulating hormones and this may indicate the following pathologies:

mental illnesses,
malfunction of the adrenal glands,
absence of gallbladder,
hypothyroidism,
pituitary tumors.

In addition, increased levels of TSH in the blood are observed in pregnant women and during prolonged, excessive physical activity. In such cases, normalization of hormonal levels occurs after the disappearance of the reasons that caused the imbalance. It is normal for pregnant women to have elevated TSH levels, especially in the first trimester, when the fetus's thyroid gland is still developing and not working properly.

If the level of thyroid-stimulating hormone is low, then this primarily indicates reduced function of the pituitary gland. Among everyday reasons that can provoke a decrease in TSH, severe psychological stress and an overdose of hormone-containing drugs should be noted. In addition, a decrease in this biosubstance in the blood can occur with the development of the following pathologies:

thyrotoxicosis,
benign formations on the thyroid gland,
brain tumors.

Norm of T4 hormone

An analysis of thyroxine levels in the blood is almost always prescribed simultaneously with a study of TSH levels. The combination of two values allows you to assess how well the thyroid gland copes with its functions. Thyroxine in the blood can be bound to proteins (albumin) or unbound (free T4). The total value is the total thyroxine, but the amount of free thyroxine is considered more informative.

Standard total T4 is measured in nmol/l. In newborn children, the highest level of thyroxine is determined, which is in the range of 69.6-219. In the age period up to 20 years, the upper limit norm gradually decreases. Therefore, the analysis results are deciphered using special tables. After 20 years, the normative range of the hormone remains unchanged and is:

for men - 59-135;
for women -71-142.

During pregnancy, overdose of hormonal medications, liver and kidney disorders, it is important to determine the level of free thyroxine in the blood in order to exclude a false diagnosis. The free T4 norm is most often measured in pmol/l and is in the following ranges:

for men - 12.6-21;
for women -10.8-22.

For pregnant women, the permissible normative values differ and change by trimester:

during pregnancy less than 13 weeks - 12.1-19.6;
during pregnancy from 13 weeks to 28 weeks – 9.6 -17;
during pregnancy 28 weeks to 42 weeks – 8.4-15.6.

The most common cause of increased thyroxine is Graves' disease. Other common pathologies that lead to an increase in the production of bioactive substances by the thyroid gland are liver and kidney diseases, obesity and benign thyroid tumors.

A decrease in thyroxine below normal is most often due to the development of thyroiditis. In addition, low T4 levels are observed with:

removed thyroid gland,
iodine deficiency in the body,
insufficient amount of protein in the diet,
lead poisoning.

Norm T3

The concentration of triiodothyronine in the blood is much lower than that of thyroxine, but its biological activity is higher. T3 affects the supply of oxygen to all tissues of the human body, accelerates protein metabolism, lowers cholesterol levels and is involved in the production of vitamin A in the liver. An analysis of the amount of triiodothyronine in the blood is usually prescribed when there is a need to clarify the condition of the thyroid gland. Total T3 is determined by the following standard ranges of values, unit nmol/l:

up to 20 years - 1.23-3.23;
up to 50 years - 1.08-3.14;
after 50 years - 0.62-2.79.

The level of free triiodothyronine is considered more indicative; its norm is 2.6-5.7 pmol/l. As the amount of free T3 increases, severe headaches and elevated body temperature may occur for a long time. External signs include hand tremors and emotional imbalance. A low level of triiodothyronine is characterized by rapid fatigue, muscle weakness and causeless cramps. Also, with a low amount of T3, sleep and brain activity are disrupted, which is manifested by slower thinking.

Indications for hormone tests and rules for taking them

If a patient turns to an endocrinologist with complaints about his condition for the first time or for the purpose of a preventive examination, the doctor will definitely prescribe the following tests to assess the functions of the thyroid gland:

on the level of thyroid-stimulating hormone,
to the level of free thyroxine,
on the level of free triiodothyronine.

This will be quite enough to draw correct conclusions about the state of the thyroid gland. The general standard for the initial examination is not indicative. If there is a suspicion of a serious pathology, then other studies may be prescribed, but the endocrinologist makes such a decision in each specific case on an individual basis. Also, the amount of bioactive substances produced by the thyroid gland may be of interest to doctors of other specializations in order to clarify the diagnosis. Indications may be:

impotence,
infertility,
arrhythmia of the heart muscle,
delayed sexual and mental development,
amenorrhea,
decreased libido.

Venous blood for analysis is always donated in the morning on an empty stomach. It is important to stop taking hormonal medications a month before the test, and three days before blood sampling to avoid taking iodine-containing medications. On the eve of the test day, you should avoid stressful situations and minimize physical activity.

Tests for thyroid-stimulating hormone (TSH), produced by the pituitary gland, and hormones produced by the thyroid gland (T3 and T4) allow an accurate diagnosis and proper treatment. Their values depend primarily on the age factor, but can also change under certain external conditions.

Many people know the main function of the thyroid gland, and the hormones produced by it are essential for the normal functioning of the body. The T3 hormone (triiodothyronine) is one of them, and the number “three” in its definition is explained by the content of exactly that number of iodine atoms in each of its molecules. It is formed as a result of the breakdown of another hormone of this gland - T4, when one iodine atom is split off from it. Being inactive, T4 converted to triiodothyronine becomes overactive. So what is this hormone and what is it responsible for? Let's try to figure this out.

How important is triiodothyronine?

T3 is a hormone that controls energy metabolic processes in the human body; it promotes the breakdown of energy and sends it to where it is needed. Thanks to its work, a person’s nerve conduction is enhanced. This hormone is also important for bone tissue and the cardiac system; it promotes the activation of metabolic processes in them.

What is free and total T3?

Gland cells are capable of producing the required amount of triiodothyronine with three iodine atoms. Having penetrated the bloodstream, this hormone binds to transporter protein molecules and is transported through the vessels to the tissues that need its work. However, a small amount of triiodothyronine, not bound to protein molecules, remains in the blood. This is the free T3 hormone.

The remaining free T3 hormone in combination with the one that is bound to proteins is called total. It is its quantity that is considered indicative in determining thyroid pathologies.

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 reproduce the hormone T3. Its amount can also increase in diseases such as diffuse toxic goiter and 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.

Norm of T3 hormone

Standard indicators depend on what equipment is used to conduct the study. Each laboratory makes its own choice in favor of certain equipment and necessary reagents. Therefore, it is impossible to define such a concept as “the norm of triiodothyronine.” Its amount is considered normal if the results obtained fall within the reference limits (from 3.15 to 6.25 pmol/l), which are indicated on the laboratory form. A form is generated on a computer, and the normal limits and amount of the hormone are determined on it.

Increased T3 hormone

Many pathological conditions of the thyroid gland are accompanied by an increase in triiodothyronine. Often a person does not even notice such a deviation from the norm. Since T3 is a very active hormone, an increase in its amount in the blood causes the following symptoms:

A person gets irritated by everything, he becomes nervous, aggressive, and gets excited very quickly. This condition is accompanied by a feeling of constant fatigue.
Fingers begin to shake.
The patient experiences increased heart rate, tachycardia, and the heart begins to work intermittently. T3 is a hormone that promotes extrasystole. A person feels this condition very well and often complains to the doctor about
The patient begins to lose weight rapidly.

Analysis to determine the level of triiodothyronine is a rather complex procedure. It is not uncommon for laboratories to make mistakes. You can additionally conduct a test to detect the level of two other hormones - T4 and TSH. If the results obtained indicate that TSH is normal and T3 is normal, this usually indicates an error.

Also, the analysis will be unreliable if the T4 value is normal, and TSH and T3 are elevated. If exactly these results are obtained, then the test should be retaken, because when the T3 hormone increases, the TSH level decreases, and T4 increases.

Decreased T3 hormone

Triiodothyronine levels may decrease if the production of all hormones produced by the thyroid gland is impaired. This condition occurs with the following diseases:

Hashimoto's thyroiditis is a disease in which a person's immune system begins to kill some thyroid cells. They cannot be restored and most often stop working and producing hormones forever.
Hyperthyroidism - this disease occurs after taking certain drugs aimed at treating diffuse and nodular toxic goiter. The most dangerous drugs in this regard are considered to be thyreostatics such as Tyrozol, Propicil, Mercazolil.
Hormone levels may decrease after surgery to remove all or just part of the thyroid gland.
also helps reduce triiodothyronine levels. This therapy is aimed at removing diffuse toxic goiter.
Hormone levels may drop when taking products containing large amounts of iodine. These include "Amiodarone", "Cordarone" and others.

But a decrease in the level of the T3 hormone in the blood does not always indicate the presence of a disease. This condition is typical for women expecting a child from 6 to 9 months of pregnancy.

You should know that the hormones T3 and T4, as well as TSH, decrease in a certain sequence. The T4 hormone level always decreases first, and only after this does triiodothyronine decrease. This happens due to the peculiarity of the body, which is protected as a result of a decrease in the hormone T3, since it is almost 10 times more active than T4.

Thanks to this, the patient does not feel the effects of hyperthyroidism so acutely. Thus, you can independently find out whether a laboratory error was made. If, according to the results of the analysis, the level of triiodothyronine is low (and it does not matter whether it is the St. T3 hormone or the total one), and T4 and TSH are within normal limits, then the data obtained should definitely be rechecked in another laboratory and the blood should be donated again.

Conclusion

Thus, deviation from is a serious pathology, which is accompanied by a change in health status. In this case, drowsiness may appear, memory and speech deteriorate, thoughts begin to get confused, and women experience disruptions in the menstrual cycle. With timely treatment, the level of hormones can be stabilized, the functioning of the thyroid gland and the whole body returns to order.

Transports iodine in the blood to the cells of the body. Reasons for changing the concentration rate:

with viral hepatitis;
when taking medications;
hypofunction of the thyroid gland.

stress, disorders;
glomerulonephritis;
liver cirrhosis;
thyrotoxicosis;
medicines.

Norms of indicators in blood tests

The normal indicators in hormone tests are:

Thyroid hormone levels will tell the specialist about the health of the gland.

But it is necessary to understand that the interpretation of the analysis will be done correctly if the gender and age of the patient are taken into account.

An important point will be the choice of analysis indicator.

Therefore, it is necessary to entrust everything to an endocrinologist, and not try to draw a conclusion based on data on the Internet.

You may be interested in:

Norms of thyroid hormone levels in women and men
Abnormalities of TSH in children: causes, symptoms, methods of correction
Normal thyroid ultrasound in children
Important and essential thyroid hormones