Thyroid UK

How long to leave NDT before blood test?

Have a blood test on Thursday, so not entirely sure how long to leave the NDT beforehand? My appointment is 8am, and I usually take my tablets 6 am and about 2-3 pm. :)

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Sip, take your morning NDT after your blood test and your afternoon dose at the usual time.

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Thanks :-)

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I would miss out the p.m. dose in the afternoon the day before your blood test as I have read that 24 hours gap is best and take dose after a.m. blood test and continue as usual.

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What about taking both doses in the morning, instead of skipping the afternoon dose?

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Try it, Sip. The idea is to leave about 24hrs after meds so that the meds aren't sloshing around your blood when you test.

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OK great. Thanks again :-)

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Yes, that's fine.

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I dont get it though?! Surely the blood test should take into account the levels we would normally have sloshing around in our bloods?

Like, if I am on T3 only and dont take it for 24 hours prior to a test then that is going to be a fairly big difference to normal, non? How then can we optimally dose? I am not arguing here, just trying to figure out how this works?

Just curious, thats all.

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Danoute, The correct reading is that which records the cellular levels of TSH and FT4/FT3 in your serum. You don't get a normal reading when you test a few hours after taking medication, you get a temporary overdose reading reflecting the level of the recently ingested medication in your blood. This can lead to dose being lowered because TSH is temporarily low and FT4/FT3 temporarily high. This also applies to other medications that need to be monitored to avoid toxicity too. I've had many repeat blood tests because of toxic result levels when I forgot to refrain from taking medication prior to blood tests.

T3 has a very short life and is usually out of your blood in 6/8 hours hence the recommendation to split dose. I always take my bedtime T3 before the next morning's thyroid test.

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