T3 24h before test

[lisan1]

My sister accidentally took her t3 (5mcg) 24 before test. How much would her true ft3 be do you think?

result 4.6 (3.5-6.5)

[tattybogle]

well , that is her true fT3 level at 24 hrs post dose. so if she is dosing once daily , that is her fT3 level at it's lowest level each day.

to see the highest level fT3 gets to you would test about 3/4 hrs post dose ., (but this peak high level in the blood does not last for very long , it goes up then down again pretty sharply over about the first 6 hrs)

so, it is usually recommend to test fT3 8-12 hrs post dose ... this misses the transient high and give a more reasonable estimate of average levels through the day.

so basically. her 'average' fT3 level over the day is obviously going to be a bit higher than this lowest level at 24hrs , but how much higher it would be at 8-12 hrs (mid point) ,,, or at 3/4 hrs (peak level) not really possible to guess.

[helvella Administrator Thyroid UK]

That is the problem!

If we (or a doctor) could work out the effects of T4 and/or T3 doses, at 12 and/or 24 hours before a test, we wouldn't need to worry. But they can't. No-one can. Too many factors in play to be able to do so.

With T3, the usual advice is to take it about 12 hours before a test. How many hours before was she intending/expecting to take her T3?

[lisan1 in reply to helvella]

She knows that now. Didnt at the time of testing. How much higher would you guess ft3 would be if 12h?

[helvella Administrator Thyroid UK in reply to lisan1]

I'd love to give you an answer. But it would not be based on science or maths. I'd have to say something like "higher than 4.6" - but that is of no help at all to you or her.

[SlowDragon Administrator]

Recommended that all thyroid blood tests early morning, ideally just before 9am, only drink water between waking and test and last dose levothyroxine 24 hours before test

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

T3 ….even if normally take as single dose

day before test it’s recommended to split T3 as 2 or 3 smaller doses spread through the day, with last dose approximately 8-12 hours before test

[lisan1 in reply to SlowDragon]

Yes, she knows that now. How much higher would you guess ft3 would be if 12h?

[SlowDragon Administrator in reply to lisan1]

No idea….depends on so many variables

Poor absorption

Gluten/dairy intolerance

Activity levels

Brand of T3

Etc etc

[SlowDragon Administrator]

also 5mcg is tiny dose

How long has she been on just 5mcg?

[lisan1 in reply to SlowDragon]

2 months