What are T3-T4 thyroid function tests?

By | 2 June 2021

What are T3-T4 thyroid function tests?

The thyroid gland, located in the neck, is the hormone-secreting gland that has many important tasks, especially the regulation of the metabolic rate in the body. Thyroid hormones called T3 and T4 are secreted from this gland and ensure that the daily functions of the body are carried out regularly. The levels of T3 and T4 hormones may go out of the normal ranges due to the malfunctioning of the thyroid gland in insufficient functioning, overworking, autoimmune thyroid diseases, and thyroid cancers. In researches for thyroid diseases, the levels of these hormones in the blood are examined by blood tests. The most commonly used thyroid function tests are T3 and T4 hormones, and to investigate the presence of autoimmune diseases, an antibody called anti-TPO or a hormone called TSH that stimulates the thyroid gland can be among the tests. If any disorder is found as a result of these function tests, further diagnostic tests and imaging techniques can be used to investigate the source of the problem in the thyroid gland.

What are thyroid hormones?

Thyroid function tests to investigate whether the thyroid gland is working well enough are applied by measuring the levels of hormones called T3, T4, T3RU, and TSH in the blood. These hormones, secreted from the thyroid gland in the neck, have important effects on many factors such as energy production and regulation of metabolic rate, weight gain or weight loss, and mood. The two main hormones produced by the thyroid gland are the T3 hormone, also known as triiodothyronine, and the T4 hormone called thyroxine. Although T4 containing 4 iodine atoms is the main thyroid hormone, it can be transformed into T3 hormone, which is formed by the removal of an iodine atom to exert its effects in some tissues. The secretion of thyroxine hormone from the thyroid gland is regulated by TSH (thyroid-stimulating hormone), a different hormone secreted from the pituitary gland in the brain. The amount of TSH secreted by the pituitary gland and released into the bloodstream is inversely proportional to the circulating T4 hormone. Therefore, if the levels of T3 and T4 hormones in the blood fall below normal as a result of insufficient functioning of the thyroid gland, the amount of TSH secreted from the pituitary gland is increased and the TSH level in the blood rises above the normal range. In some chronic diseases, during pregnancy, in people who use birth control pills and some different drugs, the levels of thyroid hormones in the blood may be affected. However, apart from these situations, the results of thyroid function tests directly show the working capacity of the thyroid gland.

In cases such as slow functioning of the thyroid gland (hypothyroidism), destruction of the thyroid gland due to autoimmune effect, or removal of a part of the thyroid gland due to various diseases, the levels of thyroid hormones in the blood are below normal and TSH is detected above normal. In this case, a picture of hypothyroidism develops, which manifests itself with symptoms such as slowing the metabolic rate and consequently weight gain, lack of energy, and fatigue. If the thyroid gland works more than normal, T3 and T4 hormone levels in the blood increase while TSH levels decrease. In this condition, called hyperthyroidism, complications such as an anxious mood, stress, palpitations, weight loss, and tremors develop. In case such differences are detected as a result of thyroid function tests, detailed examination and diagnostic tests are applied for the factor affecting the working order of the thyroid gland, and the treatment process is initiated.

What are T3-T4 thyroid function tests and when are they done?

T3-T4 Thyroid function tests consist of blood hormone and antibody tests and iodine uptake tests.

  • TSH Test: The most reliable method of obtaining information about the thyroid gland functions in the initial period is the measurement of the TSH level. As a result of this research conducted with a simple blood test, the TSH level should be between 0.4-4.00 mIU/L in healthy and adult individuals. Detection of the hormone level above this range indicates hypothyroidism, that is, insufficient thyroid functions. A low TSH level, although a rarer condition, indicates hyperthyroidism, which develops as an overactive thyroid gland.
  • T3 Test: T3 test is a blood test that is usually applied to detect the presence of hyperthyroidism or to determine the extent of the disease. In hypothyroid patients, after the TSH level rises and the T4 hormone level decreases, the last affected value is T3 hormone, so it is not diagnostic in terms of diagnosis. However, in patients with hyperthyroidism whose, TSH level is below normal, T4 hormone levels are usually normal, while T3 hormone levels are primarily elevated. Therefore, the T3 test has an important place in the diagnosis of hyperthyroidism. In healthy individuals, the level of free T3 hormone in the blood should be in the range of 2.5-5 pg/ml.
  • T4 Test: T4 hormone circulates in the blood in two different ways. The first of these is the form of T4 bound to proteins to prevent it from entering the tissues that need thyroid hormone. Another form is called free T4 (FT4), which can reach the tissues to show the effects of the hormone. While the free T4 level in the blood is low in hypothyroid patients, this value is usually above the normal range in hyperthyroid patients. Evaluation of T4 and TSH results together provides healthier results. In healthy individuals, the level of free T4 hormone in the blood should be in the range of 0.6-1 ng/dl.
  • Thyroid Antibody Tests: Under normal conditions, antibodies are produced against agents that cause disease in the body, such as bacteria and viruses in healthy individuals, and these agents are combated. In diseases also known as autoimmune diseases, the body sees its own tissues and hormones as agents and causes destruction by developing antibodies against its own tissues. Hashimoto’s thyroiditis and autoimmune thyroid disease are also included in this group, and the thyroid gland is damaged due to the autoimmune effect. To investigate whether a dysfunction detected in the thyroid gland is caused by autoimmune diseases, the blood levels of hormones such as thyroid peroxidase (TPO) and thyroglobulin are checked.
  • Radioactive Iodine Uptake Test: Thyroxine hormone contains a high amount of iodine. For this reason, the radioactive iodine uptake test, which is applied by giving radioactive iodine at a level that will not harm the body, has been developed. With this test, radioactively labeled iodine is given to the body and the path of iodine molecules in the body is examined. By examining the uptake of radioactive iodine, information can be obtained about whether the gland is functioning properly, whether there is hypothyroidism or hyperthyroidism.

How is thyroid dysfunction treated?

If a result outside the normal range is obtained in thyroid function tests, the cause of the thyroid dysfunction should be investigated. If hypothyroid patients are not treated for a long time, a picture characterized by the enlargement of the thyroid gland called a goiter and forming a swelling in the throat may occur. Apart from this, diseases that can answer the question of what is thyroid dysfunction include Hashimoto’s thyroiditis, autoimmune thyroid disease, thyroid cancer, benign thyroid gland tumors, and Graves’ disease. The way the treatment process will be planned is determined by the physician together with the determination of the factors causing dysfunction. Drug treatment is widely used in many thyroid diseases, especially hypothyroidism. In cases that cannot be controlled by drug therapy, techniques such as surgical operations and nerve motorization may be required. At the same time, the growth of the thyroid gland can be prevented by radioactive iodine treatments. In addition to medical treatment, in some patients, a dietitian may need to apply a nutrition program that is specific to the person and the disease. Depending on the type of disease, it may be necessary to increase or decrease the amount of iodine taken in the diet. In addition, foods such as cabbage, cauliflower, broccoli, brussels sprouts, radishes, and spinach, which are also known as goitrogen foods, may need to be excluded from the diet in hypothyroid patients. In these cases, patients should be directed to a dietitian by their physicians to obtain information about the nutrition plan.

If you also have a thyroid disease or if you want to undergo the necessary screenings against the possibility of any thyroid disease, you can apply to a health institution and be examined. You can get detailed information about your health status and, if necessary, your treatment plan after the necessary imaging tests and T3-T4 thyroid function tests are performed in addition to the physical examinations that your physician will perform.



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