Thyroid UK
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false blood test?

Morning all,

I've been on 75mg Levothyroxine for 4 months now as 50mg wasn't enough. Had bloods taken unexpectedly after seeing GP couple of weeks ago so had taken my Levo that morning, the results have come back as 0.30 just under lower range limit (0.35) so GP wants me to reduce to 50mg, but when I was on 50mg it wasn't enough, do you think the results are because I'd taken the Levo, normally I wouldn't have on the day of blood test.

3 Replies

More than likely. I had a test sprung on me one afternoon when I went to see the nurse and she decided to do an MOT. So I had taken my Levo and it was mid afternoon. Result came back with sky high over range FT4 and suppressed TSH (although mine always is). It must have spooked the lab as they did FT3 without being asked!

I now know to have blood drawn first thing and not take Levo for 24 hours. The next time I had to have blood taken for something the nurse said I was overdue for TFT and she'd do that too. I jumped in quick and refused to allow it. I just said "no, not thyroid today, I like to have that taken early in the morning" and she said OK, didn't question it at all.


Catalonia, tell the GP you'd taken Levothyroxine before the test and ask to stay on 75mcg and retest before you take your dose. Peak levels of thyroxine in the blood can give false low TSH and false high FT4. In any case, TSH below range does not mean you are overmedicated if FT4 and FT3 are within range.


If your GP insists on blood tests you have the right to refuse and take them when YOU are ready. Just say you are to busy or have another apointmemt that you have to keep. Doctors will spring tests when they want, my endo tried it so I never take meds before a visit. Don't do as you are told tae responsibility for yur own health.


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