Blood test timing

[Artless]

I have a 9am blood test tomorrow morning and took my usual dose of levothyroxin about 8am this morning . As suggested on this site I will not take tomorrow's dose until after the blood test. BUT I'm really clear on why I'm doing this. Does it give better results?

[greygoose]

It tells you the amount of T4 you normally have circulating in your blood. Take your dose too close to the blood draw and all you will be testing is the dose you just took, so you will have a false high FT4. Leave a longer gap and you will have a false low FT4.

[Jaydee1507 Administrator]

Partly it's for consistency the timing and when you take your last dose, otherwise it's hard to compare results. If you take your Levo just before the test, the level of FT4 goes higher as there's a fresh supply in the blood vessels. You would be measuring what you have just taken in effect. If you leave it 24hrs then you will get the results for what is the base level of T4 in the blood. Hope that makes sense!

[Artless in reply to Jaydee1507]

Yes thank you

[SlowDragon Administrator]

Just testing TSH and Ft4 is inadequate

You need TSH, Ft4 and Ft3 plus vitamin D, folate, ferritin and B12 tested

[Artless in reply to SlowDragon]

Thanks SlowDragon. Just got back from having blood test for tsh only. Apparently I shouldn't believe everything I read online. Thankfully I don't seem to be as bad as others that post here.

[SlowDragon Administrator in reply to Artless]

oh yes….we have all been told that …..😂😂😂

Just testing TSH is waste of your time and NHS money