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Thyroid UK
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Difficult question about T3 level? ......or is it!

I seem to feel well with an FT3 of about 6 in a range (3.1-6.8) having left 18hrs without meds prior to blood tests.

Does this mean that most of the time I am functioning with an FT3 level above range ?

And is that a concern?

In the distant past ( before the ERFA debacle) I had an FT3 level of 6.2 and felt terrific.

Thank you for your thoughts.x

9 Replies

I'm not much good with maths, but I think that if you feel well on a dose, then that's the right dose for you. Labs are only supposed to be a guide - doctors forget that. And lots of people need their FT3 to be slightly above range - but yours isn't even above range in the test, so Don't worry about it. :)


Thanks Greygoose, puts my mind at rest


Good. :)


GG - do you actually mean above range? I thought it was above mid-range towards the top quartile?


Some people only feel well with their T3 over range.

Optimal isn't a number, it's when all your symptoms are gone and you feel good. So if that takes you over the top of the range, so be it.


Ah, Thanks GG :)


Someone once posted a formula :-

Range 3.1 -- 6.8

6.8 - 3.1 = 3.7

3.7 x 0.75 = 2.78

3.1 + 2.78 = 5.88

So top quarter is 5.88 - 6.8

Hope I have that correct. Also remember as Diogenes said - the FT3 test results is only as good as the person interpreting it :-)


Joesmum, we're probably all over range temporarily after taking a dose of T3. The point of leaving a few hours between last dose and blood draw is to measure the circulating FT3 level rather than the peak level caused by taking T3.

If you leave 24 hours between last dose and blood draw FT3 can be extrapolated by +20% to estimate normal circulating T3. So, anyone with FT3 towards the top of range is likely to be slightly over range but, as GG said, the range is a guide.


Thanks so much everyone. Great replies....and clearly not a difficult question!!


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