Thyroid UK
84,249 members99,268 posts

Do you take your medication before blood tests?

Hi all,

I luckily found a good endo who is willing to work with me. She still wants to get my TSH up (as it is still <0.01). I am willing to work with her because she is treating my numbers AND my symptoms. I have to get bloods taken next week on my new dose and I was wondering do I take my T4 and T3 meds before the test? I've had some doctors say "yes take it so we see what the medicine is doing in your blood." And then I've had some others say not to take it. I also read that TSH will be higher if I don't take the medication? But if I don't take it, would my T4 and T3 accurately depict what this dose is doing in my blood?

Thanks in advance!

(p.s. I normally take my Levo & Liothyronine at 6:30am and get bloods around 8am).

5 Replies

I guess it's tricky to say what is 'accurate' as any test is no more than a snapshot of what's going on at that one moment in time but what is usually said here is to leave around 12hrs between meds and bloods. For me that means leaving 24hrs as like you I take my meds in the morning and I have my test the following morning. If it is longer than 12hrs just keep this in mind and adjust for it but unless your t3 is very close to the top of the range it shouldn't matter a lot.

It's great that you've found an endo you can work with but if she is trying to raise your tsh that must be her priority, not how you feel on a higher dose of meds. Just something to keep in mind if your meds are reduced and you feel unwell.

1 like

When you take thyroid hormone medication, there is a steep rise in levels - peaking somewhere around two hours later, and tailing off for several hours beyond that.

I can certainly see an argument that the height of the peak could have some interest. But on the basis that a few minutes away, you could have a significantly different result, what is that interest? It certainly cannot sensibly be compared against previous tests which were not near the peak. And how do you make sure you get that peak - rather than the shoulder of the curve either side? Bear in mind that the timing and height of that peak might well vary depending on all sorts of factors such as simple person-to-person differences, and how much binding protein is available in the blood, and whether you have had a drink or food.

We can see a parallel with this in taking blood glucose tests. You could go out and buy a device for doing them. Then sit and take repeated tests in the few hours in which you consume some food. The peak can be tracked - which we cannot ever achieve with thyroid hormones outside a lab or spedning a fortune on tests.


Hmm. Like puncturedbicycle says, the endo's focus on getting your TSH up is a bit concerning - I see from reading some of your earlier posts that you have low FT3, so it seems unlikely you're overmedicated. So make sure she has justification for any dose reductions - if your FT3 or FT4 aren't overrange then you won't be overmedicated.

For what it's worth, I firmly subscribe to the "don't take your meds before a blood test" camp. If you've just taken Levo it'll run high in your blood stream for a short while, giving a misleading picture for your FT4.


Thank you jazzw. Luckily she has been willing to reduce my Levo first and keep my T3 meds where they are, which I was comfortable with. All 3 docs I've seen since moving to the UK doubt my diagnosis because when I was diagnosed in the states, my tsh was never tested (but in past was always normal), my T4 was in range, but my T3 was lower. As a result of my tsh being "normal" they feel misdiagnosed. However I had EVERY symptom of hypothyroid. Makes me start to wonder what is right?!?!?




You may also like...