Thyroid UK
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How can I organise the gap between meds and my blood test?

I understand that I'm to leave 12hrs between my last dose of t3 and my blood draw, but I take my levo at the same time (in the morning). If I take only t3 in the morning and wait 12hrs it will be longer than 24hrs since my last dose of levo. Does that make sense? I'm going in circles trying to figure out how to space it out.

If it helps I take both meds around 7:30 every morning, and it is likely I will have the blood draw in the late afternoon/evening. (I won't have a lot of control over the timing but these are private tests so I can make allowances if the tsh is lower than it might have been if I'd been able to do the blood draw in the morning.)

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PB,

T4 and T3 can peak in the blood for up to 8 hours so as long as your blood draw is after 15.30 there shouldn't be a problem with you taking them at 7.30am as usual.

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Good news, many thanks. So there is no need to have the blood draw after 7:30 or take my t3 exactly 12hrs before the blood draw?

I used to wing it w timings but it wasn't until recently I saw this 12hr window being mentioned again and again, so I'm trying to add some consistency to blood tests in the hope it will help me interpret them w better accuracy.

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PB,

8 hours should be long enough. T3 will almost certainly be out of your blood in 6 hours.

Blood tests are a snapshot in time so testing at the same of day each time is probably the best advice. If your GP is likely to adjust your dose according to low TSH then an early morning and fasting blood test will return a higher TSH result.

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Thanks.

So can we say if your test results are over range after 6-12 hours then you're over range but any time before that and you can't count on them because the hormone is still circulating in your blood and not yet in your cells?

Just trying to understand the timing behind it a bit better.

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PB,

No, the meds may be peaking up to 8 hours after last dose but if you are showing high FT4 or FT3 12 hours after last dose you are definitely over medicated.

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Thank you Clutter.

Apologies, I don't wish to belabour the point but can you explain how the t3 can 'almost certainly be out of your blood in 6 hours' but still 'may be peaking up to 8 hours after last dose' - or are you saying it is unpredictable in a range of individuals? Sorry to be thick about this, I just want to make sure I understand. :-)

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PB,

We were talking T4 and T3 which can peak in your blood for up to 8 hours although it is likely that T3 will be out of your blood in 6 hours. These are approximations.

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Cheers, many thanks

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If I go for a blood test I don't take my meds for 24 hours but take them directly after the blood draw.

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Yes, I used to do this too and then I began to see the 12hr figure crop up again and again. Not sure what to do really, I will almost certainly be over the top after 6-8hrs, possibly at 12hrs even w no hyper symptoms at all, quite the opposite.

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