free thyroxine index


Also found in: Acronyms.

free thy·rox·ine in·dex (FTI),

an arbitrary value obtained by multiplying the triiodothyronine uptake by the serum thyroxine concentration; it largely corrects for variations in thyroid-bound globulin concentration by providing a clinically valid estimate of the physiologically active free thyroxine; direct assay or laboratory measurement of free serum thyroxine yields a more accurate value.

free thyroxine index

FT4I, T7 assay, T12 assay Endocrinology A lab value for T3 uptake combined with total T4; FTI is a clinical parameter measured by RIA, used to evaluate thyroid function, calculated by T4 x %T3RU–resin uptake; the FTI is ↑ in hyperthyroidism and factitious hyperthyroidism and ↓ in hypothyroidism; it is falsely ↑ in heparin therapy and falsely ↓ in phenytoin and valproic acid therapy, and in the euthyroid sick syndrome. See Thyroxine.

free thy·rox·ine in·dex

(frē thī-roksēn indeks)
Arbitrary value obtained by multiplying the triiodothyronine uptake by the serum thyroxine concentration.
References in periodicals archive ?
Interestingly, although the authors give importance to the free thyroxine index, which has a tendency to disappear from the diagnostic tests menu, they do not discuss the presence of heterophilic antibodies, which are increasingly recognized as interfering with thyroid function tests, nor do they mention the availability of molecular diagnostic tools.
At a trivial level, test nomenclature can be confusing (Table 1): some tests have similar names but measure different analytes, and the same test may have different names (free thyroxine index = "[T.sub.7]"; antithyroid microsomal antibody = antithyroid peroxidase).
Because oral furosemide may influence measurement of the free thyroxine index (4), the time interval between doses of oral furosemide and blood sampling should be considered in result interpretation.