Free triiodothyronine in the blood
Last reviewed: 23.04.2024
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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 |
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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 |
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