Meds before blood test: I have seen that it is... - Thyroid UK

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Meds before blood test


I have seen that it is recommended to not take levothyroxine before a blood test. Would that apply to me also ? As I have had a total thyroidectomy and I always have my blood test first thing in the morning. Thank you

18 Replies

For me the main thing is to do the same thing every time to reduce the opportunity for variation, that means I can keep better track of my numbers. I've read some supplements such as Biotin can affect your results so probably more important to leave out supplements such as that when testing.

Thank you for answering x I am not starting any supplements until after my blood test , so that won't be an issue, until I came on here 3 days ago I wasn't even aware that I should be taking supplements !

I don't have a thyroid gland either. I take my meds at night before bed. I never take them the night before blood tests. I take them straight after test in the morning then again at night. I've seen on this site that it is best to leave 24 hours between taking meds and blood tests.

Alison-Morey in reply to amala57

So what benefits do you get from taking your meds at night ? Sorry but this is all new to me x make be I should give that a go x

amala57 in reply to Alison-Morey

Hi I have to have coffee as soon as I get up!! You shouldn't have food or tea/coffee within 2-3 hours of taking levothyroxine, as it can block the uptake into your system. It suits me as I eat early in the evening then take meds just before bed. Also stops me snacking late at night! Win win!! 😊

Nanaedake in reply to amala57

You only need to leave an hour before between thyroid medication and food/tea or coffee in the morning. I cut it a bit fine by leaving 3/4 of an hour between, but that works for me. My thyroid is always suppressed. I can't take thyroid medication at night as I often have a drink before bed and sometimes eat late. You need to leave more time between food and thyroid meds if you take them at night but in the morning, after fasting through the night, an hour is enough of a gap.

One reason people do not take thyroid meds before they are tested is because they take both T3 and T4 and T3 has a rapid peak time, unlike T4, so the results could be skewed. Some people don't want their doctor to reduce their meds so they need their TSH to be at its highest level when blood is drawn. Not all doctors understand that some people need a TSH near to 1.0 to feel well. This is relevant to people with Hashimoto's thyroiditis and fluctuation in thyroid hormone. As you've had a thyroidectomy for Graves disease, just stick to the same routine, whatever you decide.

I don't have Graves disease so I don't know what TSH level suits people who've had thyroidectomy for Graves.

It is good to check vitamin levels because anyone with thyroid conditions can be low due to either insufficient absorption or too fast a metobolism and autoimmune disease can have an impact too.

amala57 in reply to Nanaedake

I feel best when tsh less than 1. I'm on t3/t4 combo.


Taking Levo should always be on an empty stomach and then nothing apart from water for at least an hour after

Taking thyroxine at bedtime suits many, even if it's just because it means you can have a cup of tea or coffee first thing in the morning . But some try it and don't like it, doesn't suit everyone

Recent research suggests it may also be more effective

Yes we should not take Levo in 24 hours before test, so if normally take at bedtime, delay until after test. If normally take on waking do the same

Ok , so might sound a bit thick of me 😂 but if I have taken this morning , do I take tonight or tomorrow night to make the change over.

SlowDragonAdministrator in reply to Alison-Morey

Personally I moved time taken backwards over 2 nights- previous 7am - next night 5am. - next about 2 am

I am extremely sensitive to changes. It was my endo suggested I try it - for me it was noticeable improvement (I never used to wait full hour before morning cup of tea)

Quite a few on here actually take in middle of night when they get up for the loo

If you have an evening out and eat/drink late then this is good option anyway

Ok that makes sense x thank you 😊

amala57 in reply to Alison-Morey

Well I had a blood test this morning. I didn't take meds last night. I took them this morning after test. I will take again tonight as normal. Back to routine. 😊

Alison-Morey in reply to amala57

And tomorrow will you feel ok ?

amala57 in reply to Alison-Morey

Yes I always have before.

The reason for leaving a 24 hour gap between levo and blood test is because doctors use TSH and Free T4 to tell them when to raise or lower dose.

TSH is affected by time of day - it has a circadian rhythm to its production - so this is the reason for doing testing by 9am at the latest.

Free T4 is affected by time since last levo dose, so to prevent a test showing a very high result and risking having dose lowered it is recommended to test after 24 hours.

It is also a good idea to fast overnight (except for water which should be drunk freely) and delay breakfast until after the blood draw.

Another reason for suggesting the above routine is that to maximise comparability between tests it is a good idea to set a particular routine for testing and stick to it.

Hi Alison, I'm with Graves, some 13 years since rai ablation - found this site about 6 months ago - there are many on here who will help you through this minefield, but do recommend that you start reading all you can about your health issues and arm yourself with information - it will take time but ultimately you will be able to take some charge of the situation and know what is best for you which may or may not be what the doctor ordered ?

Take good care, it's early days, your body needs time to adjust

Thank you so much 😊

Hello x Thank you for your reply x This forum is incredible x so many lovely, helpful people x I am feeling blessed to have found you all x

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