Free Thyroxine Index Vs Free T4. The free t4 (ft4) is available to the tissues and is, therefore, the metabolically active fraction. The free thyroxine index (ft 4 i) is the product of the measured t 4 level and the triiodothyronine uptake (t 3 u).
T4 tests t4 is the main form of thyroid hormone circulating in the blood. The normal range for the free t4 index is between 1.1 to 4.3 mcg/dl. What you really need to get out of all of this is the fact that your free t4 levels do not necessarily need to be in some magical optimal range for you to feel good.
If your results appear as high total t4 or a high free t4 index, it indicates you might be experiencing from hyperthyroidism.
A comparative laboratory study was conducted to assess the comparability of fti (free thyroxine index) and measured free t4 (thyroxine) levels in 36 euthyroid women. Free thyroxine, or free t 4, refers to a type of thyroid hormone in the body that isn’t connected or bound to certain proteins. If your results show low total t4 or a low free t4 index, it means you may have hypothyroidism. Elevations in ft4 cause hyperthyroidism, while decreases cause hypothyroidism.