False high free t4?

[Sarahlouise1980]

If i took my levothyroxine 12 hours before a blood test would it cause a false high free t4? My free t4 was 30.1 when the top of the range was 22????

[SeasideSusie Remembering]

The recommended time for last dose of Levo is 24 hours before test. Taking Levo to close to the test gives a false high, taking it longer than 24 hours gives a false low. A 12 hour gap will probably not give a massively false high but it is likely to be higher than your normal circulating level of T4.

[Sarahlouise1980 in reply to SeasideSusie]

Thanks SeasideSusie, is it likely my free t4 would have been in range had i tested 24 hours after taking it?

[SeasideSusie Remembering in reply to Sarahlouise1980]

With a result of 30.1 and top of range 22 then I doubt you would have been in range if you'd left 24 hours instead of 12. I think it may have been somewhat lower, but I don't think it would have been in range. Just my opinion of course, the only way to know for sure is to repeat the test under the advised conditions.

[Hidden]

I don't suppose you managed to have your T3 tested?

But the main thing is how do you feel?

[Sarahlouise1980 in reply to Hidden]

No I didn’t realise I hadn’t selected T3 it was a thriva test. I feel fine!

[Hidden in reply to Sarahlouise1980]

So "If it isn't broke don't try to fix it". And try not to let the doctor tinker with it either it either!