free thyroxine


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Related to free thyroxine: free thyroxine index, Free Triiodothyronine

thyroxine

 (T4) [thi-rok´sin]
a thyroid hormone that contains iodine and is a derivative of the amino acid tyrosine, occurring naturally as l-thyroxine; its chemical name is tetraiodothyronine. It is formed and stored in the thyroid follicles as thyroglobulin and released from the gland by the action of a proteolytic enzyme. It is deiodinated in peripheral tissues to form triiodothyronine (T3), which has a greater biological activity.



Thyroxine acts as a catalyst in the body and influences a great variety of effects, including metabolic rate (oxygen consumption); growth and development; metabolism of carbohydrates, fats, proteins, electrolytes, and water; vitamin requirements; reproduction; and resistance to infection. Pharmaceutical preparations of thyroxine, extracted from animals or made synthetically, are called levothyroxine.
free thyroxine the fraction of thyroxine in the serum that is not bound to a binding protein.

free thyroxine

the amount of the unbound, active thyroid hormone thyroxine circulating in the blood, measured by specific laboratory procedures. See also free thyroxine index.

thyroxine, thyroxin

a hormone of the thyroid gland that contains iodine and is a derivative of the amino acid tyrosine. The chemical name for thyroxine is tetraiodothyronine (symbol, T4); it is formed and stored in the thyroid follicles as thyroglobulin, the storage form. Thyroxine is released from the gland by the action of a proteolytic enzyme. T4 is deiodinated in peripheral tissues to form tri-iodothyronine (T3), which has a greater biological activity.
Thyroxine acts as a catalyst in the body and influences a great variety of effects, including metabolic rate (oxygen consumption); growth and development; metabolism of carbohydrates, fats, proteins, electrolytes and water; vitamin requirements; reproduction; and resistance to infection.
Thyroxine can be extracted from animals or made synthetically; it is used in the treatment of hypothyroidism and some types of goiter.

free thyroxine
the metabolically active fraction of thyroxine; abbreviated FT4, Tf. T4 = Tf + TBG. The amount is very small and difficult to estimate so that the amount present in serum is not used as a more accurate indicator of thyroxine status than T4.
thyroxine-binding globulin (TBG)
most (99.95%) of the thyroxine in plasma is bound to globulin and a small amount bound to prealbumin.
thyroxine-binding prealbumin
bound to a small fraction of circulating T4. This is the only known function of prealbumins.
L-thyroxine
References in periodicals archive ?
More specifically, a low free thyroxine at 2 and 4 weeks was associated with poorer attention skills at 3 months of corrected age as assessed by the Bayley Scales of Infant Development, Second Edition.
Based on these clinical and laboratory findings, the free thyroxine level was measured by equilibrium dialysis and found to be low.
Contract awarded for free thyroxine -ft4- 800, reagent for the determination test
The study compared 2 groups of women with free thyroxine ([FT.
0 mIU/L and normal free thyroxine (T4) and free triiodothyronine (T3) levels in the blood -- the standard definition of subclinical hypothyroidism -- had no significant differences in cognitive function and hypothyroid symptoms when compared to a healthy control group.
Propylthiouracil-induced hypothyroidism in coho salmon, Oncorhynchus kisutch: effects on plasma total thyroxine, total triiodothyronine, free thyroxine and growth hormone.
Among other changes in the leptin-treated subjects but not the controls were increases in free triiodothyronine, free thyroxine, and insulin-like growth factor-I.
Kaptein EM: Clinical application of free thyroxine determinations.
Contract awarded for code 13789 -ft4- free thyroxine, reagent for the determination test
The following tests were performed on the ARCHITECT z2000SR: thyrotropin (TSH), free thyroxine ([FT.
The need to measure free thyroxine levels has diminished in the past 2 decades, but it's still a frequently ordered test and may be an important one for some patient populations, especially pregnant women.
An important risk factor for impaired infant development is a low free thyroxine (f[T.