Before blood tests

[Islander23]

Is it ok to drink coffee or tea before a blood test? Or is it better not to?

[humanbean]

It's much better to delay. Drink water instead.

The advice we usually give on this forum for blood tests is :

a) Fast overnight (apart from water which can and should be drunk freely) and delay breakfast and morning tea/coffee until after blood has been taken.

b) If patient is taking Levothyroxine (T4), take the last dose before the test 24 hours before the blood draw.

c) If patient is taking Liothyronine (T3), take the last dose before the test 12 hours before the blood draw.

d) If patient is taking any brand of NDT (Natural Dessicated Thyroid ) such as Armour or Thyroid-S or any thyroid supplement containing animal thyroid, take the last dose before the test 12 hours before the blood draw.

e) Arrange the blood draw for as early in the morning as possible, and by 9am at the very latest.

f) Always follow the same preparation for every blood test to maximise comparability between tests.

[Islander23 in reply to humanbean]

thanks very much for this. I did take Thyroxine last night, test is at 9.30 this morning, I'll know for next time though!

[humanbean in reply to Islander23]

Your Free T4 (if it gets measured) will be higher than it would be if you'd left 24 hours between last dose and the test.

TSH will be hardly affected though. It doesn't move that quickly in response to thyroid meds. In the short term time of day for the blood draw is the important factor for TSH.

[waveylines in reply to humanbean]

Wouldnt that apply to ndt too then Humanbean as it has both T4 & t3 in it? I always fast for 24hrs before a blood test, like levothyroxine. I take a ndt.

[humanbean in reply to waveylines]

I think the rules I gave are all ones that have developed through patient experience. But consistency is probably the most important thing for comparison between tests, and it also helps when we are learning from others on the forum.

I've always assumed that the Levo, T3, and Levo/T3 combo rules are based on the fact that Levo has a long life in the body compared to T3. So testing after 24 hours for T4 and 12 hours for T3 seems to work for many people.

In the case of NDT the proportion of T4 and T3 is fixed, and obviously the T4 and T3 can't be taken separately. So which one is more important to the patient? I would argue it is the T3, so follow the rules for T3 when testing a patient who is on NDT.

If you think the above is just waffle, I would agree with you.

If you have always done your testing with different timings then it is probably more important for you to continue testing in the same way so that you can compare your tests more easily over time.

[waveylines in reply to humanbean]

Hi Humanbean...think its a case of what works for the individual I agree. My GP can get the TSH & Ft4 but ft3 has always been a battle therefore I go for the 24hr rule. That way I comply with the GPs annual test rule. The endo Im under also very good also recommends 24 hr fast.

Ive been stable for a number of years, apart from certain companies changing their ndt formula....lol. And therfore my dose is the same apart from odd temporary tweaks in cold/hot weather....

My understanding is that testing for T3 levels is a difficult area as it fluctuates far far more & quickly then T4 so testing & treating by that test is not very reliable. (Paul Robinson).

[humanbean in reply to waveylines]

A 24 hour fast??? I've never heard of that before. Did you mean a 24 hour rule?

[waveylines in reply to humanbean]

Ooops yes I meant a 24hr rule! Lol... sorry

[purple64 in reply to humanbean]

Does that apply to Carbimazole as well or just those taking Levo?

[humanbean in reply to purple64]

To be honest I don't know. I'm not hyperthyroid myself.

Clutter will probably know.

[honeypot]

Depends if it is none fasting personally I would only drink water.

[Islander23 in reply to honeypot]

Thanks Honeypot. Water it is!

[scadman]

According to my GP depends on what the blood test is for, if cholesterol or glucose, she says water only and to take any prescribed medication. For B12 no restrictions, these are the only tests I have done regularly.

[Islander23 in reply to scadman]

Thanks for replying scadman