I am in the United States but I believe this may be the test that your physician is referring to.
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.
Free T4 index (Free Thyroxine Index or FTI) is, I believe, not now performed in the UK.
Free thyroxine index
The Free Thyroxine Index (FTI or T7) is obtained by multiplying the total T4 with T3 uptake.[2] FTI is considered to be a more reliable indicator of thyroid status in the presence of abnormalities in plasma protein binding.[2] This test is rarely used now that reliable free thyroxine and free triiodothyronine assays are routinely available.
I wish they’d get rid of it here. I hate that test because the numbers are not always accurate and it makes things harder to interpret. And for some reason the emphasis is on T4, which has to be converted to T3. Its a ridiculous test. I was just hoping I could figure out what %THYR could actually be.
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