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Thyroxine (T4) is the main hormone in the thyroid gland. It acts on all tissues of the organism through the nuclear receptor. In addition, it intensifies thermogenesis and stimulates cell growth. During embryonic and infant life, thyroxine is essential for the maturation of the central nervous system.
Thyroxine – characteristics
Thyroxine is the basic hormone produced by the follicular cells of the thyroid gland, in which it is simultaneously stored and released. The necessary substrate for its production is tyrosine. Thyroxine is a molecule that is considered a prohormone and it doesn’t really matter much. Much more important is the thyroxine molecule, which does not have one iodine atom, i.e. triiodothyronine (thyroxine in the blood has a lower metabolic activity than triiodothyronine). Thyroxine deficiency causes hypothyroidism and, consequently, lowering the level of metabolism.
Thyroxine plays a role in the human body and is involved in such processes as:
- glucose absorption from the gastrointestinal tract,
- stimulating oxidation in cells,
- stimulating the breakdown of fats into glycerol and fatty acids,
- regulating lactation,
- indirect fertility regulation,
- producing somatropin and glucocorticoids.
In addition, the FT4 hormone affects the work of muscles and muscle strength and determines the proper development and functioning of the nervous system. Not infrequently, it regulates the maturation of the skeletal system (calcium-phosphate management) and affects the functioning of the reproductive system and sex glands. Thyroxine (T4) is released under the influence of TSH. In laboratory diagnostics, the hormone is also symbolized as T4 (total thyroxine content) and FT4 (free thyroxine fractions, not related to proteins).
The FT4 test is designed to check the level of thyroxine produced by the thyroid gland. When diagnosing thyroid disease, other parameters should also be taken into account. Certain relationships between FT4, FT3 and TSH have been noticed, which regulate the overall functioning of the thyroid gland.
When do we do thyroxine (T4) testing?
1. Suspicion of thyroid disorders (diagnosis of hypothyroidism / hyperthyroidism).
2. Presence of nodules in the thyroid gland (enlarged thyroid gland – goiter).
3. Abnormal TSH result.
4. Monitoring the treatment of thyroid diseases, including thyroid cancer.
5. choroba Hashimoto
6. Diseases of the pituitary gland.
7. Diagnosis of infertility in women.
- Possible symptoms of an overactive thyroid include weight loss, excessive sweating and chronic fatigue.
- Possible symptoms of hypothyroidism include: constipation, dry skin, lack of appetite, lack of energy, and bad mood. The causes of hypothyroidism can be seen in autoimmune diseases, which consist in the destruction of thyroid cells by self-produced antibodies. Diet is also important. It is recommended to consume products containing iodine, which reduces the risk of thyroid endocrine disorders.
FT4 test material: serum.
Preparation for the test: on an empty stomach (at least 8 hours). Before performing the test, inform your doctor about all medications you are taking, especially those used for a long time. The hormone therapy used will also have a significant impact on the test result.
The course of the FT4 test: one-time blood sampling from a vein in the arm. The resulting sample is sent for further analysis.
Time to wait for the result: 1 Day.
Standard: free fraction – from 10 to 31 pmol / l (0,9-2,4 ng / dl).
Comments: Only 0,03% of the total amount of thyroxine (free fraction) remains unbound with proteins (albumin, prealbumin, thyroxin-binding globulin) and exerts a physiological effect. Part of thyroxine undergoes deiodination in peripheral tissues to form triiodothyronine – so it acts as a prohormone. Thyroxine is the main hormone secreted by the thyroid gland (about 85% of the production of thyroid hormones).
In Poland, thyroid examination is performed on every newborn child. It is designed to detect possible congenital hypothyroidism. About 3-5 days after birth, blood is drawn from the heel of the newborn, and the level of FT4 and TSH is then determined. By conducting such tests, you can quickly diagnose and implement appropriate treatment to help avoid complications from hypothyroidism.
My thyroid gland – the Panaseus dietary supplement, which is available on Medonet Market at a favorable price, will help in regulating the concentration of thyroxine. Support for the functioning of the thyroid gland is also the ThyroMe Complex Health Labs supplement – daily support for the thyroid gland.
Relationship between FT4 and FT3 and TSH
The level of thyroid hormones depends on factors such as: the work of the nervous system, the work of the peripheral system and the work of the endocrine glands. TSH secreted by the pituitary gland affects the production of thyroxine and triiodothyronine. Thyroxin turns into T3 in tissues. In sick people, this process takes place not in the tissue area, but in the thyroid gland. This is due to the adaptation of the sick organism and its fight against the disease.
The ratio of T3 and T4 may change due to various circumstances and individual characteristics of the organism, while the secretion of TSH is inhibited by the concentration of T3. The mechanism that influences the relationship between FT4 and FT3 and TSH is called negative feedback. For this reason, even small changes in the concentration of T3 and T4 will cause large changes in the level of TSH. Importantly – changes in TSH levels do not affect to changes in the level of T3 and T4.
- TSH below normal and FT3 and FT4 within normal may suggest subclinical hyperthyroidism;
- free thyroxine in the norm, TSH and FT3 below the norm suggests the so-called low triiodothyronine syndrome, which may occur during a heart attack or during a high temperature;
- FT4 normal, thyrotropin below normal and FT3 above normal indicate hyperthyroidism.
Thyroxine – Interpretation of Results
1. Lowered thyroxine in laboratory tests:
- with a simultaneous elevated TSH suggests hypothyroidism,
- with reduced or within the normal range of TSH – may mean secondary or tertiary hypothyroidism.
Thyroxine deficiency can be easily regulated by supplementing with L-thyroxine, which is the left-handed form of the hormone.
2. Elevated FT4 concentration means:
- with reduced TSH level – primary hyperthyroidism,
- with elevated or within the normal level of TSH – secondary hypothyroidism.
Take care of your thyroid and order ThyroidComplex Viridian – a dietary supplement in the form of capsules available on Medonet Market.
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