Thyroid UK
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Private test for ft3 Can it wait?

Would you advice against waiting with private ft3 testing until I reached a dose with ft4 in upper limit of range?

If I order it now when I think I need to increase my levothyroxine I will need to do it again when I have reached a higher ft4.

We'll taking the test now (when not on enough levo) show me if I have a conversion problem?

3 Replies


If you take the test when you are under medicated it will simply show you are under medicated. If your Levothyroxine dose is being increased wait until you have been on the increased dose 6-8 weeks before testing. You will need TSH, FT4 and FT3 tested at the same time to assess whether you are converting well or not.

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Thank you so much for your advice. Will wait until next time then. 😊


I have read that you can only tell about conversion if you are on T4 only. As soon as you take anything with T3 in itcthen the results are teadcdifferently and the only accurate reading is the FT3 one.

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