t3/t4 testing

[Mag999]

quick question- I take all my thyroid (t3/4) medication at 6.30 am. I’m getting bloods done next week I just want to check whether I just leave it out the morning of testing, so 24+hours for both t3 and t4

Thanks

[Jaydee1507 Administrator]

The day before the test adjust Levo dose to take at same time of blood test appointment.

Split T3 into 2 or 3 and take last portion 8-12 hours before time of blood test.

If T3 is taken 24hrs before blood test then your results will show a false low as opposed to stable blood level.

[Mag999 in reply to Jaydee1507]

Thanks, that’s what I was confused about how long to leave t3

[Alternatively in reply to Jaydee1507]

Would it give an accurate result if someone was only taking only 5mcg T3 per day and they took this 5mcg in one dose, without splitting, eight hours before their 9.00am bloodtest? (That someone being myself).

So I would take my T3 at 1.00am (and my Levothyroxine at 9.00am the previous morning and again immediately after the bloodtest).

Or is it necessary to always split the T3 dose before a bloodtest?

I’d really appreciate knowing this. Many thanks for your help.

[Jaydee1507 Administrator in reply to Alternatively]

On only 5mcgs I'd still recommend splitting it into 2 if possible due to the short half life of T3. So take 2.5mcgs as usual on waking and then the last2.5mcgs around 11pm.

[Alternatively in reply to Jaydee1507]

Many thanks for your reply. So half dose 10 hours prior to bloodtest is best, not 8?

[Jaydee1507 Administrator in reply to Alternatively]

Anything between 8-12 hours. No point making it miserable and waiting up until silly o'clock.

[Alternatively in reply to Jaydee1507]

Good point, thanks Jaydee!!

[SlowDragon Administrator]

and stop any supplements that contain biotin 5-7 days before test

[RockyPath]

if you have to please a disturbed doctor who would like any excuse to cut your dose, you could stop an extra day before, which I have done. If you have enough circulating hormone to begin with, you shouldn’t feel it but TSH will rise a little bit and assuage worries of TSH-fixated clinicians.

[Ashupan]

my endocrinologist says keep taking thyroxine in morning of blood tests.. he says docs take this reading in account.

[helvella Administrator Thyroid UK in reply to Ashupan]

How do they take this into account?

The peak - typically around two hours after ingestion, is very sharp and high. Having the blood draw even a few minutes before or after the peak, rather than at the precise peak, can make a significant difference. But the person interpreting doesn't know whether your peak, with the precise tablets you take, occurs at 1:50, 2:00, 2:10, 2:30 or whenever after ingestion.

All they can do is wave their hands around a bit and say "It's fairly high but that is because you had taken the tablets." Just not good enough. The companies that make assays spend a lot of time and effort to ensure their tests are accurate to, typically, a decimal place. And some consultant comes along and uses guesswork. (Yes - we all know even the best tests have their issues.)

And how many of us are even asked "Exactly when did you take your last dose?"

I take mine at bed-time. If they don't ask, they'd very likely assume the morning, So would take it into account in the wrong direction!

[Bertwills in reply to helvella]

I wrote recently that vets use the practice of testing 6 hours after a dose of T4. I wonder why? I’m envious as it seems a much easier protocol than ours.

My dogs’s result was described as “ just above normal, which is what we like to see”. I think I’ll ask for the numbers next time. I don’t know if they use TSH results too.