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 (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.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


An elevated thyroxine concentration in the blood.
Farlex Partner Medical Dictionary © Farlex 2012


An elevated thyroxine concentration in the blood.
Synonym(s): hyperthyroxinaemia.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
Early in the course of the hyperthyroxinemia, it may not be possible to differentiate transient from persistent disease.
Familial dysalbuminemic hyperthyroxinemia; a persistent diagnostic challenge.
[1] Nonstandard abbreviations: [FT.sub.4], free thyroxine; FDH, familial dysalbuminemic hyperthyroxinemia.
Abnormal [T.sub.4] binding to [T.sub.4] -binding prealbumin (TTR) is a rare cause of euthyroid hyperthyroxinemia. Moses et al.
These findings confirmed the diagnosis of dysprealbuminemic hyperthyroxinemia.
Euthyroid dysprealbuminemic hyperthyroxinemia is a rare disorder, which in this patient was coincident with hyperthyroid Graves disease.
Familial dysalbuminemic hyperthyroxinemia and thyroid hormone autoantibodies: interterence in current free thyroid hormone assays.
The poor degree of agreement between the [FT.sub.4] and TSH values in our study might be attributable in part to transient hyperthyroxinemia that did not last long enough to induce a decrease in TSH to <0.15 mIU/L.
Euthyroid familial hyperthyroxinemia due to abnormal thyroid hormone binding protein.
Hyperthyroxinemia. Abnormal binding of Tq by an inherited albumin variant.
Results of liver-function tests, serum protein electrophoresis, immunoglobulins (G, A and M), thyroid-hormone-binding globulin, anti-thyroidmicrosomal and anti-thyroglobulin antibodies, screen for familial dysalbuminemic hyperthyroxinemia, and anti-[T.sub.4] and anti-[T.sub.3] antibodies were normal.
All patients had normal concentrations of thyroid-binding globulin, a negative screen for familial dysalbuminemic hyperthyroxinemia, and no anti-[T.sub.4] and anti-[T.sub.3] antibodies.