Thyroid UK
87,712 members102,405 posts

Do I take thyroid meds before blood test

Hi All just a quick question. I have got thyroid blood tests in the morning at 9am I'm going early because also having a cortisol blood test and that's to be done at 9qm Apparently. Do I take my thyroid medication or not? It's a question I've wondered for a while. I would usually have my medication about 5am if I'm awake if not sometimes between 9 and 10am. I take 150 Levo and 12.5mcg of T3, I do usually take them together not even sure if I'm suppose to do that or wether I have to take separate. The main thing is do I take any of them in the morn. 😀

15 Replies
oldestnewest

No

1 like
Reply

Take your Levo and T3 right after your blood tests.

1 like
Reply

If you take your meds before you test then your FT3/4 will be artificially inflated. Thyroid tests should always be the earliest possible test and by 9 at latest to get highest TSH ( as that is what many GPs pay most attention to). It follows a circadian rhythm and drops through the morning.

You should also do a fasting test with water only until after the test, no supplements first either. Some labs use a biotin assay in the test so it is as well to leave out any supplement containing biotin for a few days to avoid it potentially skewing the results.

Gps say itdoesn't matter whether you have eaten, taken meds or test late. They are wrong, it can be the difference between a dose raise or cut sometimes if you tend to be borderline.

There is no problem taking your T3 and 4 at the same time but don't take supplements with them too as they can effect absorption of thyroid meds

1 like
Reply

Hi - don't take them before. For future tests - too late for this one - you need to change your time of taking t3 beforehand so that it is ideally 12 hrs before test with down to 8 ok. 24 hrs is too long for t3.

2 likes
Reply

The procedure for blood tests is the very earliest possible, fasting (you can drink water) and allow a gap of 24 hours from your last dose and the test and take levothyroxine afterwards. This keeps the TSH at its highest as doctors are apt to adjust dose due to the TSH alone and don't check any other important thyroid hormones.

1 like
Reply

No no no no never ever take your thyroid meds in the 24 hours before a blood test

2 likes
Reply

That does of course just mean t4, the question also relates to t3.

Reply

Its still easier to not take t3 in previous 24 hours just like t4 because no one knows for sure what time it takes to clear the bloodstream ...different people react differently

In some people leaving 48 hours from last dose of T4 is only way they get an accurate test

If doctors insist on relying on TSH alone and fail to understsnd the biology of the pituarity thyroid feedback loop ....that compounds the problems

Reply

Standard advice and "policy" in this forum- as advised by all administrators and resident experts - is to leave gap of 24-36 hrs from last t4 dose before test and 8-12 (ideally close to 12) after t3 dose. Your advice is contrary to that and has the potential to cause confusion.

You are correct about doctors and their lack of knowledge, however we are where we are and all we can do is work the system as best we can with our superior knowledge!

Gillian

Reply

Right so when reading your time gaps between meds and blood test then I shouldn't be taking my T4 and T3 at the same time like I do is that right? 🤔

Reply

It is no problem taking them together normally, I do. The only change is when you are going into a test. you really need to take t3 at night for a couple of nights prior, you can then revert to taking it in the morning again if that suits you.

This is because t3 hangs around in blood for a shorter time than t4, so to take it more than 12hrs before would give an inaccurate, probably falsely low, result for ft3.

Gillian

1 like
Reply

Oh dear well it's too late now. Maybe I should of sent this post last week 🙄 Thankyou for your advice

Reply

when my lot were on both T4 and T3 they would take the t4 in the morning and the T3 later in the day

but everyone has a different biology and whats right for one is not always right for another

on NDT obviously that's taken twice or 3 times a day in split dose but again some people only take it in the morning

I do know that when on T3 alone both my husband and daughter and granddaughters had to leave at least 24 hours before a test or their GP would start trying to mess with their dosages

They are all now on NDT and their GPs know that TSH is thus irrelevant plus they all have Central Hypothyroid

1 like
Reply

I'm hoping to get on to NDT tbh reallyfedup coz I'm really fed up of Levi I think it's like poison

Reply

Thankyou all for your replies. Really appreciated

Reply

You may also like...