Thyroid hormones

By right, the thyroid gland is considered to be one of the most important organs in the human body. The thyroid gland weighs about 20 grams. However, such a small organ is the provider of vital energy to the body of any person.

The thyroid gland controls the activity of almost all organs and systems with the help of the produced iodine-containing hormones.

Without sufficient number of thyroid hormones such processes are impossible:

  • Normal metabolism.
  • Growth, maturation of tissues, organs and bone apparatus.
  • Energy nutrition of cells and the whole organism.

Free triiodothyronine (FT3) is a biologically active part of triiodothyronine (thyroid hormone), which is not associated with blood plasma proteins and regulates the rate of basic metabolism, tissue growth, metabolism of proteins, carbohydrates, lipids and calcium, as well as the activity of the cardiovascular, digestive, respiratory, reproductive and nervous systems.

Free thyroxine (FT4) is one of the two main hormones of the thyroid gland, it’s main function is the regulation of energy and plastic metabolism in the body. Free thyroxine is the biologically active part of the common thyroxine, which plays an important role in the metabolism.

Thyroid stimulating hormone (TSH) is the main regulator of thyroid function, synthesized by the pituitary gland – a small gland located on the lower surface of the brain. Its main function is to support a constant concentration of thyroid hormones that regulate the processes of energy production in the body. When their content in the blood decreases, the hypothalamus releases a hormone that stimulates the secretion of TSH by the pituitary gland.

Dysfunction of the pituitary gland can cause an increase or decrease of thyroid-stimulating hormone level. With an increase in its concentration, thyroid hormones are released into the blood in abnormal amounts, causing hyperthyroidism. With a decrease in the thyroid-stimulating hormone level, the production of thyroid hormones also decreases and symptoms of hypothyroidism develop.

The causes of disruption of the production of thyroid-stimulating hormone may be a disease of the hypothalamus, which begins to produce increased or decreased amounts of thyreoliberin, a TSH secretion by the pituitary gland. Diseases of the thyroid gland, accompanied by a violation of the secretion of thyroid hormones, can indirectly (by feedback mechanism) affect the secretion of thyroid-stimulating hormone, causing a decrease or increase in its concentration in the blood.

Antibodies to thyroid peroxidase (ATPO) are autoantibodies to this enzyme.

Until recently, these antibodies were called antimycrosomal (AMA) because they were associated with the microsomal fraction of thyroid cells. Modern studies have identified that thyroid peroxidase is the main antigenic component of microsomes.

Determination of antibodies concentration to TPO is one of the most sensitive tests for the diagnosis of autoimmune thyroid diseases. Autoimmune diseases of the thyroid gland are the main factor underlying hypothyroidism and hyperthyroidism, and usually develop in genetically predisposed people. The presence of increased titer of antibodies to TPO and a higher level of TSH make it possible to predict the development of hypothyroidism in the future.

The highest level of antibodies to TPO is identified in patients with Hashimoto’s thyroiditis. In this disease, antibodies to TPO are found in about 90% of cases, which confirms the autoimmune nature of the disease. These antibodies are also often detected (60-80%) in patients with Graves’ disease. There is a clear link between the presence of antibodies to TPO and the histological picture of thyroiditis. However, in connection with the considerable ability of the thyroid gland to regenerate under the action of a thyroid-stimulating hormone, the clinical signs of hypothyroidism may appear years after the onset of a chronic thyroid disease.

The determination of antibody titer to TPO helps in the diagnosis of autoimmune thyroid diseases and allows differentiating autoimmune diseases and non-autoimmune goiter or hypothyroidism. Investigation of antibodies to TPO (thyreperoxidase) is usually carried out together with the study on TSH.

Antibodies to thyroglobulin are specific immunoglobulins directed against the thyroid hormone precursor. They are a specific marker of autoimmune thyroid diseases (Graves’ disease, Hashimoto’s thyroiditis).

Thyroglobulin is a glycopeptide, a precursor of triiodothyronine (T3) and thyroxine (T4). It is produced only by the cells of the thyroid gland and accumulates in its follicles in the form of a colloid. With the secretion of hormones thyroglobulin in a small amount gets into the blood. For unknown reasons, it can become an autoantigen, and the body produces antibodies to it in response, which causes inflammation of the thyroid gland. ATTG can block thyroglobulin, disrupting the normal synthesis of thyroid hormones and causing hypothyroidism, or, on the contrary, over-stimulating the gland, causing its hyperfunction.

Antibodies to thyroglobulin simultaneously interact with the components of the connective tissue of the eye socket, eye muscles and the acetylcholinesterase enzyme. It is possible that the autoimmune reaction is the cause of changes in the orbital tissues in thyrotoxic ophthalmopathy.

ATTG is found in 40-70% of patients with chronic thyroiditis, in 70% of patients with hypothyroidism, in 40% of patients with diffuse toxic goiter and in a small number of patients with other autoimmune pathologies, including pernicious anemia. Although, healthy people have a slightly higher level of antibodies, especially in case of older women.

Mainly the test for ATTG is useful when confirming the patient’s diagnosis of “diffuse toxic goiter” and / or “hypothyroidism due to autoimmune thyroiditis.” In addition, it is valuable in the differential diagnosis of Graves’ disease and toxic nodular goiter. Despite the fact that ATTG is less frequently detected in the blood serum than thyroid microsomal antibodies (antibodies to peroxidase), for patients with autoimmune thyroid diseases the results of this analysis are also important for confirmation of the diagnosis.

If a pregnant woman has an autoimmune thyroid disease or some other autoimmune pathology, a test for one or more thyroid antibodies should be scheduled at the beginning of pregnancy and shortly before the birth to predict a risk of newborn’s thyroid failure.

10051. “Thyroid hormones” test package №1

  • Free Thyroxine (FT4)
  • Free Triiodothyronine (FT3)
  • Antibodies to thyroid peroxidase (ATPO)
  • Thyroid-stimulating hormone (TSH)

10052. “Thyroid hormones” test package №2

  • Free Thyroxine (FT4)
  • Free Triiodothyronine (FT3)
  • Thyroid-stimulating hormone (TSH)

 

10053. “Thyroid hormones” test package №3

  • Free Thyroxine (FT4)
  • Antibodies to thyroid peroxidase (ATPO)
  • Thyrod-stimulating hormone (TSH) 

10054. “Thyroid hormones” test package №4

  • Free Thyroxine (FT4)
  • Thyroid-stimulating hormone (TSH)

10055. “Thyroid hormones №5” test package №5

  • Free Thyroxine (T4 St.)
  • Free Triiodothyronine (T3 pers.)
  • Antibodies to thyroid peroxidase (ATPO)
  • Thyroid-stimulating hormone (TSH)
  • Antibodies to thyroglobulin (ATTG)

10056. “Diagnosis of thyroid nodules” test package 

  • Antibodies to thyreperoxidase (Anti-TPO)
  • Antibodies to thyroglobulin (Anti-TG) Tireoglobulin (TG)
  • Thyroid-stimulating hormone (TSH)
  • Cancer-embryonic antigen (CEA)

10059. “Diagnosis of autoimmune thyroid diseases” test package

  • Antibodies to thyreperoxidase (Anti-TPO)
  • Antibodies to thyroglobulin (Anti-TG)
  • Thyroid-stimulating hormone (TSH)