According to my reference book, the FTI or T7 test (apparently equivalent designations) is a mathematical calculation used to correct the estimated total thyroxine (T4) for the amount of thyroxine-binding globulin (TBG) present. In order to make the calculation, the lab finds the total T4 value and the T3 uptake ratio, and multiplies them together. “The FTI is useful in the diagnosis of hyper- and hypothyroidism, especially in patients with known or suspected abnormalities in thyroxine-binding protein levels. In such patients, blood levels and clinical signs may seem contradictory unless both T4 and TBG are considered as interrelated parameters of thyroid status.” And “The free thyroxine index permits meaningful interpretation by balancing out most nonthyroidal factors.” (From A Manual of Laboratory & Diagnostic Tests, 5th edition, by Frances Fischbach).
So, there isn’t a thyroid hormone called T7, and I haven’t a clue why the test is designated as such.
Bobbi
