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Thyroid UK
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A question about blood test timing

As this is the first blood test since starting T3 my GP has requested tsh, ft4 and ft3. We both laughed about the possibility of the the ft3 being done but he’s put on the form that I take liothyronine so you never know!

I take my T4 and T3 all in 1 go at night as that works best for me but if I don’t take it until after my bloods it will be 36 hours.

I could take the T3 earlier but food/other meds timings would be a hassle.

Your thoughts please?

10 Replies

It's nice you can have a laugh with your GP.


It is indeed. It makes a big difference finding a decent one is a rare thing x

1 like

Usual recommendation is 12 hours before for T3

24hours for T4

So take T3 little earlier and delay T4 until after blood draw

If you are taking vitamin B complex, or any supplements containing biotin, remember to stop these 3-5 days before any blood tests, as biotin can falsely affect test results




Thank you x


Very important info - thanks! Do you stop any other supplement before blood test - iron etc?


You leave off iron for 5-7 days. Most others you don't have to leave off but take after your blood draw on the day of your test.


Thanks! 😄


HI there

I've just been told by my GP that they won't prescribe Liothyronine (they did for the past two weeks but the surgery partner has caught on and said they won't any longer). They will be refer me to an Endo but in the meantime, I can't have any more (even if that means I'm meds-free in the meantime!). I see that your GP prescribes it to you. Have you had a problem getting it?

Best wishes



I don’t have it prescribed I source my own at the minute. I’m hoping to persuade the endo when I go back in January though as it is just starting to make a difference. If not it’s a small price to pay for getting my life back.

My Gp knows I take it and is quite happy to monitor me as he agrees that some people need move than levothyroxine. I’m very lucky to have such a good Doctor who treats people as individuals not just illnesses x


I think the problem is more cost than anything else. I've been researching online since I got back from the docs and lots of policy docs from CCGs instructing GPs to stop prescribing. I've been paying for Armour Thyroid for years which is very expensive but my third consultant is retiring and it's not easy to find someone who will prescribe it. My problem is T4 to T3 conversion so T4 alone won't work. Please let me know what your endo says. I'm hoping to be referred to one who is sympathetic. I've been well for 10 years on T4/T3 and was like a zombie for three years before getting it sorted. Good luck. x


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