T4/Free T4

T4/Free T4



Basic Information image



Definition




• Hyperthyroxinemia: Increased circulating concentration of thyroxine


• Hypothyroxinemia: Decreased circulating concentration of thyroxine



Synonym(s)


Thyroxine



Typical Normal Range (US Units; SI Units)




• T4: 16.39 to 23.35 nmol/L


• Free T4: 10.15 to 12.95 pmol/L



Physiology


Thyroxine (or 3,5,3′,5′-tetraiodothyronine) is the major hormone secreted by the follicular cells of the thyroid gland. T4 is transported in blood, the majority being protein bound, principally to thyroxine-binding globulin (TBG), and to a lesser extent transthyretin and serum albumin. T4 not bound to proteins is referred to as free T4 (fT4) and is the biologically active form. T4 is involved in controlling the rate of metabolic processes in the body and influencing physical development. fT4 enters most cells where it is converted to T3.



Causes of Abnromally High Levels


Typically due to a functional neoplasia of the thyroid gland resulting in increased production of the hormone. However, exogenous administration of thyroid-stimulating hormone (TSH) or thyroid-releasing hormone (TRH) could also cause a physiologic increase in circulating hormone concentrations as well as administration of iodide containing compounds.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on T4/Free T4

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