T3 - thyroid hormone: what is responsible, the norm and the deviations from the norm

Many people know the main function of the thyroid gland, and the hormones produced by it are extremely necessary for the normal functioning of the body. The hormone T3( triiodothyronine) is one of them, and the figure "three" in its definition is explained by the content in each molecule of that very number of iodine atoms. It is formed as a result of the dissolution of another hormone of this gland - T4, when one iodine atom is split off from it. Being inactive, transformed into triiodothyronine T4 becomes excessively active. So what kind of hormone is it and why does it respond? Let's try to figure this out.

How important is triiodothyronine?

t3 hormone

T3 - a hormone that controls the body's energy exchange processes, it promotes the decay of energy and sends it to where it is needed. Thanks to his work, the person's nerve conduction increases. Also important is this hormone for bone tissue and cardiac system, promotes the activation of metabolic processes in them.

What is T3 free and common?

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t3 free

The gland cells are capable of producing the required amount of triiodothyronine with three iodine atoms already. Penetrating into the bloodstream, this hormone binds to the molecules of protein-transporters and is transported through the vessels to tissues that need its work. However, a small amount of triiodothyronine, not associated with protein molecules, remains in the blood. This hormone T3 is free.

The remaining free hormone T3 in combination with that associated with proteins is called generic. It is its number is considered indicative in determining the pathology of the thyroid gland. What is the purpose of the analysis for the hormone T3?

To determine the state of the thyroid gland, the endocrinologist necessarily gives the patient the direction for blood tests for three hormones - TTG, T4, T3.A trial for triiodothyronine is considered very important, since it minimizes the diagnostic error.

glands and hormones

For example, quite often working nodes in nodal toxic goiter reproduce the hormone T3.Its amount can increase and with such diseases as diffuse toxic goiter and Basedova disease. If the result of the analysis 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 the hormone T3

hormone assay T3

The norm values ​​depend on what equipment is used for the study. Each laboratory makes its choice in favor of certain equipment and necessary reagents. Therefore, it is impossible to define such a concept as the "triiodothyronine norm".The amount of it is considered normal if the results obtained fit within the reference boundaries( from 3.15 to 6.25 pmol / l), which are indicated on the laboratory blank. A form is formed on the computer, and the limits of the norm and the amount of the hormone are determined on it.

Increase of the hormone T3

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 - a hormone is very active, increasing its amount in the blood causes the following symptoms:

  • The person is all annoyed, he becomes nervous, aggressive, very quickly excited. This condition is accompanied by a feeling of constant fatigue.
  • You start to shake your fingers.
  • The patient has an increased heart rate, tachycardia, the heart begins to work with interruptions. T3 - a hormone that contributes to the occurrence of extrasystole. Such a person feels very well and often complains to the doctor for malfunctions in the work of the heart.
  • The patient begins to lose weight rapidly.

hormones т3 and т4

Analysis of the determination of the level of triiodothyronine is a rather complicated procedure. It is not uncommon for laboratories to make mistakes. You can additionally carry out a test to reveal the level of the other two hormones - T4 and TSH.If the results obtained indicate that TSH is normal, and T3( the hormone) is elevated, this usually indicates an error.

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

Lowering of the hormone T3

The level of triiodothyronine may decrease in case of disruption of the production of all the hormones that are produced by the thyroid gland. This condition occurs with the following diseases:

  • Hashimoto's thyroiditis is a disease in which human immunity starts to kill some thyroid cells. They can not be restored, and most often they cease to work and produce hormones.
  • Hyperthyroidism - such a disease occurs after taking some drugs aimed at treating diffuse and nodular toxic goiter. The most dangerous means in this regard are such thyreostatics as "Tyrozol", "Propitsil", "Mercazolil".
  • The level of the hormone can be reduced after surgery for removing the entire thyroid gland or only part of it.
  • Treatment with radioactive iodine also helps to reduce the level of triiodothyronine. Such therapy is aimed at removing diffuse toxic goiter.
  • The level of the hormone can fall when you receive funds containing a large amount of iodine. They include "Amiodaron", "Kordaron" and so on.

Std3 hormone

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

It should be noted that the hormones T3 and T4, as well as TSH, decrease in a certain sequence. The first is always a decrease in the level of the hormone T4 and only after this falls triiodothyronine. This is due to the peculiarity of the organism, which is insured as a result of the decrease in the hormone T3, since it is almost 10 times more active than T4.

Due to this, the patient is not so keenly aware of the consequences of hyperthyroidism. Thus, you can independently determine whether a laboratory error has been committed. If, according to the analysis results, the level of triiodothyronine is lowered( and it is not important whether it is a T3 hormone or a common hormone), and T4 and TTG are within normal limits, then the data obtained should be rechecked in another laboratory and donated blood again.


Thus, the deviation from the norm of thyroid hormones is a serious pathology, which is accompanied by a change in the state of health. At the same time, drowsiness may occur, memory and speech become worse, thoughts start to get confused, women have a malfunction in the menstrual cycle. With timely treatment, the level of hormones can be stabilized, the thyroid gland and the whole organism work in order.