How much does taking levo before a blood test affect the TSH result? Or is it more important for T4?

My doc sprang a blood test on me last week (went about something else!) but I'd taken my levo about 2 hours before as I wasn't expecting it. I have never taken it before a test before and the result has come back TSH 0.09 (0.27 - 4.2). It was 0.13 a couple of months ago so I don't know if taking my tablets was signficant or not.

Many thanks,


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6 Replies

  • It can make a significant difference. Helvella posted a link recently but I didn't bookmark it. If your GP tries to reduce your dose on the basis of the test explain that you'd taken medication and ask that any decrease should be deferred until after your next TFT.

  • Thank you, I will do that. They did bloods for a few things and apparently some need repeating so hopefully they'll recheck my tsh too, I'll ask for it if they weren't planning to.

  • Has anyone got the link to hevellas post. I missed that one.

  • Your doctor can suggest but cannot force you to have any treatment or tests. Next time politely refuse any blood tests after you have taken meds.

  • Ah well, it was for other things and it was only afterwards that he said it'd check my thyroid as well! So if he does try to reduce on the basis of it I will ask for a repeat and explain why (not that he'll probably believe it makes a difference but hey!)

  • You do not need to explain yourself, he should know that you should not take meds before a blood test. JUST SAY NO!!

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