Early morning blood test

[130396]

can anyone tell me if having a blood test at 5.30 am would be a problem for tsh ft4 and ft3?

would the results be skewed

[Jaydee1507 Administrator]

TSH is highest at 9am so try for a blood test as close to then as you can get. I'm not sure I could even get anyone to do me a blood draw at 5.30am. Remember to time taking your Levo the day before to allow 24hrs before the blood test.

[tattybogle in reply to Jaydee1507]

It's highest around midnight/1am (ish) .. then in falls until it's lowest around 1-3pm ..

so 5.30 am result will probably be a bit higher than 9 am .

However , there is no point trying to get a high TSH by doing a private blood test at 5.30 am ... for 2 reasons:

1) when the NHS test , it won't be at 5 .30 ( 8/9 am will usually be the earliest draw you can possibly get) , so your GP's results will be lower than the private one , and GP will be using their own results for making diagnosis / adjusting dose , not private ones.

2) the reference ranges for TSH tests are made using "daytime" samples (taken eg 9-5 ish) .. a 3/4/5 am result cannot be interpreted correctly using daytime ref ranges .. if you wanted to correctly interpret a 3/4/5 am sample, you need to compare it to healthy TSH taken at 3/4/5 am , so you'd need a 'night time' TSH ref range . which no one has made.

Due to the pulsatile way TSH is released , it's not possible to be certain that 9 am will be higher or lower than 8.30am or 9.30 am ... see these close ups .. the line is up and down in little pulses, which will of course vary quite a bit between individuals ... researchgate.net/figure/Pul...

[130396 in reply to tattybogle]

this isn’t for me. It’s got my friend who is getting her colleague to test . But has to have it done at 5.30 am so the person that’s drawing her blood can get off to work.

What I’m asking is if the tsh ft4 ft3 will be higher or lower at 5.30 am compared to an 8.30am draw

[tattybogle in reply to 130396]

see below

[tattybogle]

TSH/ fT4 / fT3 all move over the course of the day and night, (and if taking thyroid hormone, then the timing of the last dose needs to be taken into account too)

So you won't be able to accurately compare a 5.30 am blood test with blood tests taken at other times ..... just as you can't accurately compare a 9am blood test to a 3 pm blood test.

thyroidpatients.ca/2020/07/... circadian-rhythms-tsh-f4-f3/

[tattybogle]

Basically .. you would not expect to see a huge difference in any of these between 5.30 to 9 am .. but she needs to be aware that:

her 9am TSH will probably be a little bit lower.

her 9 am fT4 will probably be a little bit higher .

Her 9 am fT3 might be a bit lower/ or it might be about the same.

So for example 5.30 am results may give the impression that she is more hypothyroid ( Higher TSH / lower fT4 )....... whereas 9am results would look closer to euthyroid (normal)

[130396 in reply to tattybogle]

thank you.

I’ll pass this onto her