Best time of day for blood test: Hiya, does it... - Thyroid UK

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Best time of day for blood test

Jenbot78
Jenbot78

Hiya, does it make a difference in terms of accuracy what time of day I test? I have a Thriva blood test kit. Thanks

12 Replies
oldestnewest

Hello!

The same rules apply as if you were having a "professional" blood draw........do it early ie. 8am.

On an empty stomach having had no food since the previous evening. You can drink water (no tea or coffee) freely, in fact being well hydrated is recommended, it makes the blood flow better and be less "sticky".

If you normally take your levo or T3 in the morning take it after you have done your sample.

If you normally take at bedtime do not take your dose the night before but take it after your sample and resume regular dosing that evening.

Do the sample on a Monday, Tuesday, Wednesday or at a push Thursday (use guaranteed next day signed for delivery in this case). You do not want your sample festering in the postal system over the weekend!

Hope this helps!

SeasideSusie
SeasideSusieAdministrator

Jenbot78

The only thing I would add to spongecat's reply is:

If you take levo then leave 24 hours between last dose and blood draw.

If you take T3 or NDT then leave 8-12 hours between last dose and blood draw.

Any longer and you get false low results for FT4 and FT3, too close to blood draw and you get false high results for FT4 and FT3

meme
meme
in reply to SeasideSusie

How would TSH be affected by stopping meds the day before or taking less meds for a few days before a test? Would it make a lot of difference?

SeasideSusie
SeasideSusieAdministrator
in reply to meme

meme

It's not TSH that's affected by leaving off Levo for 24 hours. It's FT4. As explained to Jenbot above, timing of Levo affects the hormone level - FT4. Levo peaks in the blood 2-6 hours after ingestion. If you take your Levo (which is T4) close to your blood draw, the test will reflect that and give you a false high. If you take your Levo too far away from your blood draw then again that's reflected and you get a false low. To measure the normal circulating amount of T4 then a gap of 24 hours between last dose of Levo and blood draw is advised.

TSH takes a long time to change if dose of Levo is changed.

meme
meme
in reply to SeasideSusie

Thank you.

I still wonder how quickly TSH moves up or down over a week say, as it goes up and down at different times of the day. Has anyone had it tested a few times over a couple of weeks and seen it change?

SeasideSusie
SeasideSusieAdministrator
in reply to meme

meme

The only personal experience I have of a change in TSH level is when an endo wanted mine back in range (it was always below range).

He reduced my Levo and my level went from 0.02 to 0.4 (0.27-4.20) and it took 3 months. That was reducing Levo from 125mcg to 100mcg.

Hi

I recently had a blood test that came back with high TSH 3.5 yesterday despite me tripling the dose of levo since early Dec when it was 3.99. This is important to me as I am waiting to do IVF and they won’t proceed until I get below 3.0. I take my dose at night. The night before my test I took my normal dose just a few hours earlier. I tested at 8:30am. Do you think this could have impacted the results? I have been reading here perhaps I should have skipped my dose the night before altogether? Thanks in advance. Should I ask for a retest?

SeasideSusie
SeasideSusieAdministrator
in reply to NJB1418

No, I don't think it would have impacted the TSH result. TSH is slow to react to change of dose, as illustrated in my reply above to Meme.

TSH has a circadian rhythm anyway and is highest very early morning and lowers throughout the day, i.e. highest at midnight, lowest around 1pm then rises again. See first graph in this thread healthunlocked.com/thyroidu...

Eating before a test may lower TSH, drinks containing caffeine affect TSH.

Timing of Levo before the blood test determines the result for FT4 as mentioned in a previous reply in this thread.

If you want members to comment on your situation, you would be best starting your own thread, mentioning in the title about pregnancy/IVF/TSH to attract the attention of those in a similar position. It is unwise to try and fiddle a false low TSH for pregnancy, you need a true reading for lower TSH for successful conception and pregnancy.

Thanks for your response. Apologies for posting in wrong place I’m pretty new to the forum. I appreciate the advice. Rest assured I would never try and ‘fiddle’ something which may impact my ability to have a baby.

Thanks a lot everyone! I took my last dose this morning at about 8am so will aim to do my test at 7 and then take my tablets afterwards

Hi Jenbot. Only just found out about Thriva testing & wondered if you've used before ? Is it a finger prick test ? Grateful to hear anything about Thriva. Are they are Laboratory. Do they do other tests ? 😊

Hi Jenbot, regarding my previous message - have just found article on Thriva Testing, so now more informed 😊 Just a little unsure about them supplying a subscription service ? Does this mean once you order a test with them, you have to have any suggested follow up tests done thro them ?

Also have read bloods are analysed by NHS , would it follow that results are kept on patient NHS record ?

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