When free thyroxine cannot be measured directly, the free thyroxine index (FT₄I) may be calculated by using which measured laboratory data?

Question

Quizplus · Accepted Answer

The free form of thyroid hormone is the physiologically active form of the hormone.Considering T₄, fT₄ can either be estimated by (1) measuring total thyroid hormone concentration plus some measure of binding protein concentration and calculating a free thyroid hormone index or (2) by a direct measure of the free thyroid hormone concentration.In this situation when free T₄ cannot be measured, it can be estimated by the following equation:
FT₄I = total T₄ × T₃ resin uptake
The T₃ resin uptake serves as the measure of binding protein concentration.

When Free Thyroxine Cannot Be Measured Directly, the Free Thyroxine