Blood test

Hormones
1

Hi

I should know this having been on treatment for years but put it down to brain fog !

Should thyroxin dose be taken or not before a blood test

Thanks

2

Hello

I am always advised to have my blood taken before my dose to get a truer reading of blood level of thyroxine.

3

I have seen this discussed many times - and it pretty much always ends up asking what result do you want?

If you are having fT4 tested then for a few hours after taking your thyroxine it will be distinctly high.

If you are having TSH tested then it is supposed to be slow to change and would not matter - but I am not convinced. So, in my opinion, if you are worried about your TSH being too low, definitely do not take before your test. If you are worried about your TSH being too high, take thyroxine before the test.

Overall, I think you get a more reasonable picture by delaying your thyroxine until after the blood has been taken.

4

US guidelines state that you should not take your meds when about to have a blood test.

I believe it is a minimum of nine hours before a test, so that would always mean taking the medication the day before. I think this applies even more so when taking T3.