Free T4 index

This test helps doctors evaluate your thyroid function.

Free T4 index Overview

Reviewed: April 22, 2014

Indirect measure of free T4. Corrects for high/low values of thyroxine-binding globulin (TBG).

The normal ranges for free T4 index are the following:

  • Males: 1.5 - 3.0
  • Females: 1.3 - 3.0


Blood draw

What the results mean

In healthy individuals, the free thyroxine index (FTI) remains relatively constant.

Higher than normal free T4 index indicates hyperthyroidism.

A lower than normal free T4 index indicates hypothyroidism.