Free Thyroxine Index Vs Free T4. Free thyroxine comprises a small fraction of total thyroxine. As such, it can sometimes be difficult to determine.
Normal ranges for free t4: When pituitary or hypothalamic disease is at fault, the tsh may be low or normal. 1 distribution of free thyroxine values in seven groups ofsubjects.
The free t4 (ft4) is available to the tissues and is, therefore, the metabolically active fraction.
It is sometimes referred to as t7. While total t4 is a relatively reliable indicator of t4 levels in the presence of normal binding proteins, it is not a reliable indicator when binding proteins are abnormal. The free thyroxine index (ft 4 i) is the product of the measured t 4 level and the triiodothyronine uptake (t 3 u). The frequency distribution of free t4 values were comparable for the oc users and the nonusers.
