Beckman Coulter Access Free T3 Reagent, 100 Determinations, 2 x 50 tests

Specifications

Brand: Access®

Manufacturer: Beckman Coulter

Country of Origin: United States

Application: Reagent

Number of Tests: 100 Tests

Test Name: Free Triiodothyronine (T3)

Test Type: Thyroid / Metabolic Assay

Intended Use

The Access Free T3 assay is a paramagnetic particle, chemiluminescent immunoassay for the quantitative determination of free triiodothyronine levels in human serum and plasma using the Access Immunoassay Systems.

Summary and Explanation

The hypothalamic pituitary-thyroid axis controls thyroid hormone synthesis, release, and action. Thyrotropin-releasing hormone (TRH) secreted from the hypothalamus stimulates the synthesis and release of thyrotropin or thyroid-stimulating hormone (hTSH). hTSH, in turn, stimulates the synthesis, storage, secretion, and metabolism of thyroxine (T4) and triiodothyronine (T3).

T3 is the major biologically active thyroid hormone. Of the circulating T3, about 80% is formed from peripheral deiodination of thyroxine and 20% is secreted directly from the thyroid gland. The T4 and T3 hormones are transported in the circulation bound to thyroxine binding globulin (TBG), thyroxine binding pre-Albumin (TPBA) and albumin. About 0.2 to 0.4% of the circulatory total T3 is in equilibria as unbound or free, in contrast to about 0.03% of the total T4. In most individuals, the free fractions of these hormones correlate with the functional thyroid state.

Free T4 and T3 regulate normal growth and development by maintaining body temperature and stimulating calorigenesis. In addition, free T4 and free T3 affect all aspects of carbohydrate metabolism as well as certain areas of lipid and vitamin metabolism. Fetal and neonatal development also require thyroid hormones.

With normal levels of thyroid binding proteins, free T3 levels correlate with total T3. Measuring free T3 is useful when altered levels of total T3 occur due to changes in thyroid hormone binding proteins, especially in cases with altered TBG or low albumin concentrations. Free T3 is elevated alone (T3 toxicosis) in about 5% of hyperthyroids.

Non-thyrometabolic disorders may cause abnormal free T3 levels. Determination of thyroid status in patients with non-thyroidal illness (NTI) should be interpreted with caution. For example, anticonvulsant drug therapy (particularly phenytoin) may result in decreased free T3 levels due to an increased hepatic metabolism, and secondarily to displacement of hormone from binding sites. Anti-inflammatory drugs such as salicylate and phenylbutazone also compete for hormone binding sites, but their effect on free T3 levels has not been clearly defined. Patients on heparin therapy may have elevated free T3 levels due to release of non esterified fatty acids (NEFA), which can alter the relationship between free and bound hormones.