What's included in a thyroid profile test: Free thyroxine index; T3 uptake (THBR); thyroxine (T4)


FTI stands for the Free Thyroxine Index and it is an estimation of the free T4 concentration

• Total thyroxine (T4). Most of the thyroxine (T4) in the blood is bound to a protein called thyroxine-binding globulin. Less than 1% of the T4 is free. A total T4 blood test measures both free and bound thyroxine. Free thyroxine affects tissue function in the body, but bound thyroxine does not.
• Free thyroxine (FTI or FT4). Free thyroxine (T4) can be measured directly (FT4) or calculated as the free thyroxine index (FTI). The FTI tells how much free T4 is present compared to bound T4. The FTI can help tell if abnormal amounts of T4 are present because of abnormal amounts of thyroxine-binding globulin.
• Triiodothyronine (T3). Most of the T3 in the blood is attached to thyroxine-binding globulin. Less than 1% of the T3 is unattached. A T3 blood test measures both bound and free triiodothyronine. T3 has a greater effect on the way the body uses energy than T4, even though T3 is normally present in smaller amounts than T4.

https://www.webmd.com/women/thyroid-hormone-tests#1

Photo credit: http://ancestralmomentum.com/2011/12/takin-a-peek-under-the-hood-hackin-my-bloodwork/

 https://www.labcorp.com/test-menu/35801/thyroid-profile#

Sample lab report: https://www.labcorp.com/sites/testmenu/files/000455.pdf

Lab interpretation: https://www.labcorp.com/tests/related-documents/L964

Resources:
https://www.webmd.com/women/thyroid-hormone-tests#1