A bit confused

HU mentions that when having a thyroid blood test early in the morning, you should not eat only have water and leave taking the thyroxine pill that morning. The nurse who took my blood at 11.30am my having had my breakfast and tablet had never heard of this. I had in fact phoned the reception days beforehand and they said the same. I have two friends with under active thyroid for some years and they too have never been told not to. Was my blood test a waste of time then and where does this advice come from?

[SlowDragon Administrator]

NHS guidelines and thyroid specialist endocrinologist advice

Average GP has absolutely no idea

Similarly if taking any supplements that contain biotin you need to stop these 5-7 days before test as biotin can falsely affect test results

Rare to find GP or nurse that’s aware. There are a few notices now in some phlebotomy departments re biotin

[Hidden in reply to SlowDragon]

Thank you so much for your reply.

[greygoose]

Well, doctors have never heard of it. But, then, their 'education' - if you can call it that - in thyroid is very, very limited. Plust doctors seem to lack any logic at all.

So, where does it come from? Basically, the early morning blood draw comes from doctors' ignorance and obsession with the TSH. The TSH varies throughout the day and is highest before 9 am and at its lowest around midday. For some weird reason doctors don't know this and believe that the time of day doesn't matter. But, if you want an increase in dose, and have the blood draw at midday, it matters a lot! To get that increase - and not a decrease! - you want that TSH as high as possible! Also, eating, and especially drinking tea or coffee, before the blood draw, can reduce the TSH level, which is not what you want.

FT4 levels peak in the blood around 2 to 4 hours after taking levo. So, if you have your blood draw during that time, all you are measuring is the dose you just took, and the FT4 will be very high. So, once again, you risk a reduction in dose. What you want to know is your normal circulating level, which you will get by leaving a gap of 24 hours from your last dose of levo to the blood draw.

So, it all comes from a healthy dose of logic, and knowing a little bit about how all this works.

[Hidden in reply to greygoose]

That makes more sense, appreciate your reply.

[greygoose in reply to Hidden]

You're welcome.

[Ellie-Louise in reply to greygoose]

So my TSH of 0.03 is at its highest at 08:30, what on earth is it later on in the day, non-existent?

[serenfach in reply to Ellie-Louise]

Probably a bit lower, but it does not matter. What matters is your T3 and T4 in that order. The guy who actually invented the TSH test said it was pretty useless if you take any thyroid drugs. I have no idea why the TSH is now considered the gold standard by GPs and Endos - they have it wrong.

[greygoose in reply to serenfach]

Well, it does matter if you have a doctor obsessed by TSH, because that's about all they look at. They don't understand the rest. Which is why we always advise getting tested when TSH is as high as it can be.

[greygoose in reply to Ellie-Louise]

Possibly, yes. Especially if you're taking T3. But, as serenfach said, it doesn't make any difference to you, only to your doctor. We don't care what our TSH is once it gets below 1. But doctors take it as a sign of over-medication, they just don't know any better.

[Batty1]

Not uncommon for medical people to not be familiar with this information and if your friends don’t look stuff up they won’t know this either….. I fast for every test and delay my meds because doctors just don’t know and so many things can interfere with labs.

[tattybogle]

See first 2 replies from me on this post for evidence / reasons for having early am test/ 24hrs from last dose: healthunlocked.com/thyroidu....