What is the reason for low free T3?

The first thing I want to explain to you is that free T3 is a type of amino acid in the body, which is a cellular substance synthesized in the thyroid gland. If the free T3 level is low, it cannot directly reflect the function of the thyroid gland because it is not active. Friends who want to know the status of their thyroid function should test the amount of FT3, because it is not bound to protein and is not affected by other secretions. The thyroid gland is an important secretory organ in the human body. If there is any problem with it, it will have a huge impact on the body's endocrine system.

1. What is the reason for low free t3?

T3, also known as triiodothyronine, is an iodine-containing tyrosine that is synthesized in thyroid gland cells using iodine and tyrosine as raw materials.

Thyroxine is a hormone synthesized and secreted by thyroid follicular cells. It is released into the blood circulation in a free form, and most of it quickly binds to plasma proteins. The bound part of triiodothyronine (T3) and tetraiodothyronine (T4) has no biological activity, and its level cannot reflect the functional state of the thyroid gland. Only a small part of it is not bound to the protein and is in a free state, which is called serum free triiodothyronine (FT3) and serum free thyroxine (FT4). Both of them can most directly reflect the functional status of the thyroid gland and are not affected by changes in the concentration and binding capacity of thyroxine-binding globulin in the blood.

Low TSH means that your body secretes too much thyroid hormone, but T3 and T4 are normal. Do you feel uncomfortable at ordinary times? Eating too much iodine-containing substances will not cause high TSH, but will reduce it instead. It is recommended to eat less iodine-containing substances and then have a thyroid function test. The thyroid gland is located in the neck. Clinically, hyperthyroidism presents symptoms such as swollen neck, heat intolerance and sweating, palpitations and irritability, rapid hunger, impatience and irritability, tremors of fingers and tongue, and weight loss. It is a multiple-organ disease.

2. Causes of free t3 production

When the thyroid gland is acted upon by TSH and releases thyroid hormone, the glandular epithelial cells first ingest the thyroglobulin in the follicular cavity into the glandular cells through pinocytosis. Under the action of lysosomal protease, the thyroglobulin is decomposed. The released T4 and T3 can resist the action of deiodinase and have small molecules, so they can enter the blood circulation through the capillaries. The amount of T4 on the thyroglobulin molecule far exceeds that of T3, so T4 accounts for about 90% of the total hormone secreted. The amount of T3 secreted is less, but its activity is greater, 5 times that of T4.

3. Clinical significance of free T3

If serum TT3, TT4, FT3, and FT4 increase, especially TT3, it is hyperthyroidism. In a few patients, only serum TT3 is elevated, while serum TT4 is still within the normal range. In a very small number of patients, serum TT4 is elevated, while TT3 is not significantly elevated.

If serum T T3, T T4,

If FT3 and FT4 decrease, especially FT4 decreases significantly, it is hypothyroidism. In a small number of patients with hypothyroidism, serum T T4 is reduced, while serum T

T3 can be within the normal range.