When to take T3 before blood test - advice please. - Thyroid UK

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When to take T3 before blood test - advice please.

Tasker profile image

This week I'll be doing my next Medichecks blood test for TSH, T4 and T3. I do the blood tests at around 8am. I take 100mcg levothyroxine at bedtime and I know I need to miss the dose the night before testing.

I also take 5mg T3 in the morning. Last time I did my bloods, I took the T3 the morning before as usual and then did the blood test the next day at 8am before taking that day's dose of T3. But from what I've learnt on this forum, it seems the the ideal is to take the previous T3 dose 12 hours before the test, not 24 hours before, to get a sense of the average T3 level in the blood. So should I take my T3 in the evening the day before rather than in the morning, even though that's different to my usual routine?

Grateful for any advice from those more experienced than me! Thanks.

12 Replies
SeasideSusie profile image
SeasideSusieAdministrator

When booking thyroid tests, we advise:

* Book the first appointment of the morning. This is because TSH is highest early morning and lowers throughout the day. If we are looking for a diagnosis of hypothyroidism, or looking for an increase in dose or to avoid a reduction then we need TSH to be as high as possible.

* Fast overnight - have your evening meal/supper as normal the night before but delay breakfast on the day of the test and drink water only until after the blood draw. Eating may lower TSH, caffeine containing drinks affect TSH.

* Leave off Levo for 24 hours before blood draw, if taking NDT or T3 then leave that off for 8-12 hours. Take after the blood draw. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results.

These are patient to patient tips which we don't discuss with doctors or phlebotomists.

I take Levo plus T3 and I alter the timing of my dose of both the day before to accommodate the time gap that's advised here.

Tasker profile image
Tasker in reply to SeasideSusie

Thank you; v helpful to know you adjust the timing of your doses the day before doing blood tests. That sounds like what I should do.

SlowDragon profile image
SlowDragonAdministrator in reply to Tasker

Because you take Levo at bedtime, you need to alter timing before testing

If for example taking blood test Monday morning at 9pm, on Saturday night delay Levo dose until Sunday morning

On Sunday morning delay T3 dose until 9pm (unless trying to get increase in T3...... in which case perhaps take T3 Sunday morning as per usual)

Tasker profile image
Tasker in reply to SlowDragon

Thanks for that clarification. I'd not known to delay the levo dose before (I'd just missed the dose the night before testing) so will start doing that for this and future tests, and will also adjust the T3 timing as you've both suggested. The T3 is self medication and it's really the effect of that I want to find out (I have previous results for just the 100mcg levo) so am looking to get the T3 result as accurate as possible rather than as low as possible, if you see what I mean.

SlowDragon profile image
SlowDragonAdministrator in reply to Tasker

Yes, when normally taking Levothyroxine at bedtime, if you just delay Levo until after test then that's too long a gap.....it's 36 hours not 24

Yes if self medicating T3, you want to know actual true result, so taking T3 around 9pm day before

You might notice improvements in sleep by taking T3 near bedtime

Tasker profile image
Tasker in reply to SlowDragon

Thanks, SlowDragon. It will be interesting to see the effect on my sleep.

SlowDragon profile image
SlowDragonAdministrator in reply to Tasker

It was through changing dose timing before blood test that I discovered how much moving last fish to later dose time helped

I now take T3 waking, mid afternoon and bedtime (8 hour gap between each dose).

Tasker profile image
Tasker in reply to SlowDragon

That's food for thought. I'm at the stage now of fine tuning my dose, and perhaps experimenting with timing will be part of the answer to getting things as good as they can be. I'm currently taking just 5mcg T3 (alongside 100mcg levo) and that's a quarter of a 20mcg tablet so I can't divide it any further, so will need to take all the T3 at once - but will see if taking it in the evening is better than the morning (have just taken it!).

SlowDragon profile image
SlowDragonAdministrator in reply to Tasker

I take 20mcg- 10mcg, 5mcg and 5mcg

When I first started I did cut initial 1/4 dose into into 2 x 1/8ths

I use a small craft knife/scalpel to cut up

Tasker profile image
Tasker in reply to SlowDragon

Ah, ok. I've just been using a normal kitchen knife! Will get something more suitable ☺️.

SlowDragon profile image
SlowDragonAdministrator in reply to Tasker

Something like this

In most art shops

ebay.co.uk/itm/1-Set-Metal-...

Tasker profile image
Tasker in reply to SlowDragon

Thanks!

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