(redirected from hyperthyroxinaemia)


 (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.


An elevated thyroxine concentration in the blood.


An elevated thyroxine concentration in the blood.
Synonym(s): hyperthyroxinaemia.
References in periodicals archive ?
Once increased thyroxine-binding protein (TBG), presence of antibodies connected to T3 and [T.sub.4], amiodarone treatment, familial dysalbuminaemic hyperthyroxinaemia (FDH), high-dose or intermittent L-thyroxine treatment which are among other causes of inappropriate TSH release are ruled out, THR and TSHoma should be investigated (1), (2).
Causes of discordant thyroid function test results Raised TSH with a normal or Low TSH with a normal or low raised FT4 FT4 Subclinical hyperthyroidism Subclinical hyperthyroidism Recent treatment of Recent treatment of hypothyroidism hyperthyroidism NTI (recovery phase) T3 toxicosis Drugs Drugs (steroids, dopamine) Interfering antibody NTI Resistance to thyroid hormone Pituitary disease Central hyperthyroidism Normal TSH with a raised FT4 Normal TSH with a low FT4 Intermittent T4 therapy NTI Interfering antibodies Recent treatment of hyperthyroidism Familial dysalbuminaemic Interfering antibody hyperthyroxinaemia Central hyperthyroidism Pituitary disease
familial dysalbuminaemic hyperthyroxinaemia) or antibody interference with measurements of FT4, FT3 or TSH.
Potential causes of spurious TFT results include nonspecific binding of endogenous circulating factors, such as heterophilic antibodies, with assay reagents (1), the presence of albumin variants found in familial dysalbuminemic hyperthyroxinaemia (2), and thyroid hormone autoantibodies (THAA) (3).We describe a patient who had discordant TFTs due to circulating THAA and report differences in TFT results obtained on a variety of automated immunoassay platforms.
A screening test for familial dysalbuminemic hyperthyroxinaemia (4) was also negative.
Eighteen subjects (4.2%) had a TSH level lower than 0.4 [[micro]unit]/ml; two of them had hyperthyroxinaemia; another was taking thyroid hormone for hypothyroidism.
Nuclear binding and cellular metabolism of thyroxine in a euthyroid patient with hyperthyroxinaemia. Clin Endocrinol (Oxf) 1983;18:251-7.
Hyperthyroxinaemia in hepatocellular carcinoma: relation to thyroid binding globulin in the clinical and preclinical stages of the disease.