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Free triiodothyronine in the blood

 
, medical expert
Last reviewed: 29.07.2022
 
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Reference values (normal) CT 3 (triiodothyronine) in blood serum - 4-7,4 pmol / l.

On cT 3 (triiodothyronine) accounts for 0.3% of its total amount in the blood. Fraction cT 3 (triiodothyronine) provides the entire spectrum of metabolic activity. CT 3 (triiodothyronine) is a product of the metabolic transformation of T 4 (thyroxine) outside the thyroid gland. It should be emphasized that the deiodination of T 4 with the formation of T 3 (triiodothyronine) is more intense in the anterior pituitary gland than in the peripheral tissues. In connection with this, the determination of the serum level of cT 4 is of great importance in assessing the state of regulation of thyrotropic hormone secretion by the feedback principle. Contents Ct 3 (triiodothyronine) does not depend on the concentration of TBG, however its definition very informative for evaluation of thyroid status changing TBG content.

The determination of the concentration of cT 3 (triiodothyronine) is justified in the initial diagnosis and long-term monitoring of patients with thyrotoxicosis developed in iodine deficiency , in which suppression of the formation of thyroid-stimulating hormone is possible with isolated hyperproduction of only T 3 (triiodothyronine) and unchanged T 4 (T 3 -toxicosis) . In conditions of mild iodine deficiency, this condition is often observed in diffuse toxic goiter (up to 25% of cases). In the case of hyperthyroidism, the concentration of cT 3 increases, and decreases with hypothyroidism.

Diseases and conditions in which the concentration of cT 3 (triiodothyronine) in the blood serum changes

Increase in concentration
Reduction in concentration

Thyrotoxicosis, lack of iodine

Condition after treatment with radioactive iodine preparations

Endemic goiter

Pendred's syndrome

The use of estrogens, oral contraceptives, methadone, heroin

Postoperative conditions and severe diseases

Hypofunction of the thyroid gland

Acute and subacute thyroiditis

The intake of androgens, dexamethasone, propranolol, salicylates, coumarin derivatives

trusted-source[1], [2], [3], [4], [5], [6]

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