How long to leave NDT before blood test? - Thyroid UK

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How long to leave NDT before blood test?

sip1 profile image
sip1
9 Replies

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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sip1
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Clutter profile image
Clutter

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

sip1 profile image
sip1 in reply to Clutter

Thanks :-)

shaws profile image
shawsAdministrator

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.

sip1 profile image
sip1 in reply to shaws

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

Clutter profile image
Clutter in reply to sip1

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.

sip1 profile image
sip1 in reply to Clutter

OK great. Thanks again :-)

shaws profile image
shawsAdministrator in reply to sip1

Yes, that's fine.

Danoute profile image
Danoute

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.

Clutter profile image
Clutter in reply to Danoute

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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