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Thyroid UK
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Taking meds before a blood test

How do test results differ if you take your meds T4/T3 on the day? I recently upped my meds from 175mcg to 200 mcg T4 and 20mcg to 10mcg T3 cause I’m pregnant.

At my booking in appointment my midwife gave me a blood test when I’d taken my meds that day already. Normally I don’t take them the day of a test.

The results were the same as before I upped my meds. Does that mean I’m under medicated still?

FT4 14.7 up from 14.5

FT3 3.7 stayed the same

13 Replies
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I think the point is that the test is reading the dose you have just taken rather than what will be in your bloodstream later in the day. The usual advice is leave off t4 for 24 hrs and t3 for 8 to 12 hours. I think it is always going to be a bit hit and miss because your hormone levels rise and fall naturally through out the day and with t3 in particular it has a relativly short half life. The advantage of following the usual advise is that you can compare your results to previous ones. I would have expected your ft3 to be higher.

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How long was the gap between taking the meds and the blood draw?

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It was 2 hours max! I just know I feel awful and the blood results don’t reflect any kind of increase. I haven’t been referred to a consult yet so I’m more or less self medicating till I do

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Well, it's possible they hadn't had time to be fully absorbed - certainly not the levo. But, you're right, the levels should be higher on those doses. How do you take your hormone? Do you take it on an empty stomach and wait an hour to eat or drink? Do you take any other medication of supplements with them?

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Yes on an empty stomach and wait. No other meds at the same time

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How long were you on that dose - 200 mcg levo and 20 mcg T3 - before the test was done?

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About 2 weeks.

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Well that was much too soon. You don't have accurate results in any sense of the term. Wait six weeks and try again. You gave yourself a massive increase, there - you shouldn't actually have increased by that much all in one go, it will take time to sort itself out.

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25mcg is standard increase

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25 mcg of levo, yes, but not with 10 mcg T3 at the same time. And, you should only increase T3 by 5 mcg at a time. :)

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You misunderstood. I increased Levi but lowered T3. I was on 20mcg and lowered to 10mcg cause didn’t want to risk going about range

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Ah, ok. The way it was written was rather confusing. :)

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I lowered my T3 from 20 -10mcg cause I didn’t want to risk going above range and not knowing if they were gonna take me off it altogether during the pregnancy but wonder if I should go back to 20 mcg

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