My Endos View On Measuring FT3: Just had to share... - Thyroid UK

Thyroid UK

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My Endos View On Measuring FT3


Just had to share this with you (from one of the Endos on the list....)

I take 30mcgs T3 and 25mcgs T4.


It is quite difficult to interpret TFTs when someone is on a combination of T3 and T4 replacement.

The best scenario would be to check TSH and try and keep it in the middle of the reference range. The measurement of FT3 levels will not add much significant information as they are short acting medication and the levels can be variable based on the timing of the day and the dose and hence is not a good guide to change therapy.


6 Replies

This is too simplistic an idea. If you take both T4 and T3, then the T3 comes from a combination of direct T3 supply and T4 conversion to T3 by the body. This means that the conversion controls the level of T3 much more and partly smooths out any fluctuations caused by direct T3 intake. The situation with pure T3 is quite different as there is no conversion to smooth out the spike in T3 immediately after you take it. However, even then, if you are tested at a fixed time every time, after taking the last medication, ideally about 4-5 hours after, there will be more consistency in the measurement values for FT3. TSH in mid range MIGHT be OK with joint therapy, but I'd rather it was in the lower part of the range around 0.8-1.5. In combination therapy, and T3 therapy, the "healthy" TSH range is more appropriate, where it isn't on T4 monotherapy.


This was written in a letter from Endo to my GP. No wonder GP doesn't have a clue! Or Endo!

shawsAdministrator in reply to paulaelizabeth

Thank God for Researchers/scientist like diogenes who knows what he is talking about.

It is such an uphill battle to educate the Professionals as they've no clue about what to do or how best to treat patients so that they have relief of clinical symptoms and feel well.

My TSH has never been as high as 0.8 even when my free t3 and free t4 were under range - not everyone's pituitary responds in a textbook fashion.

That sounds like absolute rubbish. Very, very few healthy people have a TSH in the middle of the reference range and no one taking T3 would. Why not just measure free t3 and symptoms? Simples! TSH varies up to 75% according to time of day (and possibly year) so how is that any better? And we don't all have an optimally functioning pituitary and hypothalamus. Sounds like quackery.

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