Ideal blood test timing for T3?

[London3891]

Hello,

I routinely follow the advice on this forum to have blood tests done first thing in the morning, after fasting and before taking Levothyroxine (so blood draw is about 25.5 hours after my last dose).

I'm now adding 5μg of T3 which I've been told to take in the morning along with T4. Given that T3 has a shorter half-life, when would it make sense to take the last dose before blood tests? My endocrinologist has said "at least two hours after", but I'm not sure whether to take the T3 really early in the morning without the T4, or whether to take the last T3 dose the night before (rather than in the morning as prescribed), or whether to just take it the morning before.

Any advice gratefully received!

[SeasideSusie Remembering]

London3891

We always advise last dose of T3 should be 8-12 hours before the blood draw, splitting the dose the day before even if we don't normally do that.

If I was taking 5mcg - and presumably that is a 5mcg tablet - I'd take 2.5mcg in the morning and 2.5mcg 8-12 hours before the test (I tend to go for the middle and do 10 hours).

Take last dose of Levo as you would normally do when testing, i.e. as close to 24 hours before test as you can.

After the test take that day's dose as normal.

[London3891 in reply to SeasideSusie]

Thank you, SeasideSusie. Annoyingly the 5mcg is actually a quarter of a 20mcg tablet (apparently all that the pharmacy can order...and I'm trying to pick my battles!)

It's already difficult to get even quarters, so trying to cut the tiny tablet into eighths could be a challenge! That said, since it's already pretty inaccurate, maybe I should just give it a go

[SlowDragon Administrator]

5mcg is very unlikely to be high enough dose

On day before blood test, cut the 1/4 tablet in half....it will be speck of dust....take 2.5mcg at 7am.....and 2.5mcg at 9pm (assuming test at 9am)

Likely to need at least 2 x 5mcg at roughly 12 hour intervals

[London3891 in reply to SlowDragon]

Thank you, SlowDragon!

Out of interest, I just came across this in the accompanying leaflet - could be a way of trying to get a more accurate dose. It means wasting 3/4 of every tablet though, which seems a bit crazy (especially given the cost argument often used for not prescribing T3).

T3 dosing instructions

[SlowDragon Administrator in reply to London3891]

It’s rubbish....invented to try to use up more tablets

Imagine pharmacy if you took the waste T3 liquid back for disposal (it should not be tipped down sink )

Everyone just cuts T3 into 1/4’s with pill cutter or craft scalpel

Only about 1% of tablet is active ingredient