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December 3, 2022

Free Thyroxine Index Isn't Completely Free

The free thyroxine index (FTI), also called T7, is a calculation based on total T4 levels and T3 uptake. It was an early method used to detect hypothyroidism or hyperthyroidism without the interference of variations in thyroid binding proteins.

A decreased FTI suggests an insufficiency of T4 and hypothyroidism, while an increased FTI suggests an excess of T4 and hyperthyroidism. 

Although FTI has largely been replaced by direct measurement of free T4, it may be used to help diagnose central hypothyroidism caused by dysfunction of the pituitary gland which produces the TSH that stimulates thyroid hormone production.

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Tag(s): Biomarkers

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