I'm sure I'm missing something here, but I saw this article (pubmed.ncbi.nlm.nih.gov/578... posted a few days ago by another member, which suggests that TSH levels are lowest in the morning, and thyroid hormone levels are highest in the morning:
"TSH: A diurnal rhythmicity could be demonstrated with peaks from 8 p.m. to 2 a.m and a nadir from 7 a.m. to 2 p.m"
"Thyroxine: Pooled data showed peak values from 8 a.m. to 12 a.m"
"Triiodothyronine: Hormone levels were highest from 7 a.m. to 1 p.m"
I've read countless times on this forum that the advice is to get bloods tested no later than 9am in the morning (fasting and delaying medication) in order to show the highest possible TSH levels, and the lowest possible FT4 and FT3 levels.
This study seems to suggest the exact opposite - can anyone shed any light?
Thanks
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London3891
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"TSH: A diurnal rhythmicity could be demonstrated with peaks from 8 p.m. to 2 a.m......
say's TSH highest at a time between 8pm and 2am ... highest in middle of night .... but we can't advise people to get blood taken then, cos everywhere is shut.
....... and a nadir from 7 a.m. to 2 p.m"
says it's lowest from 7am to 2pm... this looks a little confusing because it mentions 7am ,,, but it means it starts to fall at 7 am , and gets to its lowest around 2pm... which is true and this is exactly why we say to get the earliest blood test possible ... as soon as the Doctors is open, because it's falling slowly all the time throughout the morning.
Obviously if you were doing your own test and didn't need a nurse to draw the blood, you could get a higher TSH level if you took the blood at 3 or 4 am... but that 's not very practical. And wouldn't be possible to replicate with any official bloods done by the doctors because they can't do them at that time .. so it wouldn't do us any good to go waving a private blood test at the Doctor with a TSH from 3am.. because when he tested it himself to confirm it would have to be during opening hours and so it would be lower and he'd send you away with a flea in your ear.
The part about lowest possible fT4 and fT3 levels ... we never say the reason for early am blood draw is for lowest T4 and T3 levels .. we say it's to get highest TSH.... because we are advising re. getting a diagnosis ,, ands TSH is the first that is being looked at by NHS. If the TSH is in range they don't look what the fT4 is.
Basically you can't get a blood test to show both .. you have to pick which you want...if you want to show lowest T4/3 then the time for that will also be the time that TSH is lower.... So Dr will say ... TSH in range ...go away.. no diagnosis
If you want to show highest TSH in order to help getting a diagnosis then the time for that will also be the time that T4 /3 are higher.. there's no way round this . it's just the way it works... The TSH peaks are followed a short while later by peaks in the fT4 and fT3, because the TSH spurt has made the thyroid produce T4/3 in response.
There isn't a way to show lowest TSH and lowest fT4 and lowest fT3 on the same blood draw... it's not possible.. so we pick the most useful... which in an NHS system that is (unfortunately) TSH based for diagnosis and dose adjustment, means earliest possible am blood draw is the best option.
edit * the above applies to tests for diagnosis when we are not taking thyroid hormones.
Once we are taking thyroid hormones the diurnal rhythm is blunted a bit, ( probably due to takingT4 all in one lump) and we can now influence the fT4 level by adjusting the time of the last dose Levo in relation to the time of test. There will be a big spike in fT4 in the blood about 4/5 hours after swallowing the Levo.. so we avoid this by taking last dose a long way away from that ... simplest rule for consistency is "24 hrs from last dose and take next dose immediately after blood draw"
(It's slightly more complicated if taking T3 as well, but basically "12 hrs from last dose T3" ,i think)
Hopefully someone will come along and post the graphs showing TSH/T4/3 measured every half hour or so over a 24 hr period....i can't find where i've put them.( SeasideSusie has linked them below . thankyou )
(But it's not a steady line up and down though the day.. it's more like the edge of material cut with pinking shears .. little peaks and trough's every hour or so because they are all secreted in a pulsatile fashion )
The 'eating lowers TSH' thing is a bit dubious... the research took the 2nd measurement (after eating) at a later time in the morning .. so TSH would have been lower anyway.
But even if it's not proven, i don't have breakfast on blood test days.. just in case it makes a difference, and i like to keep everything the same so i can trust the comparison from last time. And it's easier to remember No breakfast , than it is to remember What i had for breakfast last time.
I think it should also be said that the difference between the highest and lowest points of FT4 is a lot narrower than the highest and lowest points of TSH. So, the fact that the FT4 is highest at the same time as the TSH is highest, doesn't make an awful lot of difference to anything. Hope that makes sense.
What does make a difference to the FT4 is the gap between the last dose of levo and the blood draw, and we always say to leave 24 hours for that reason.
I've read countless times on this forum that the advice is to get bloods tested no later than 9am in the morning (fasting and delaying medication) in order to show the highest possible TSH levels, and the lowest possible FT4 and FT3 levels.
I am one of the responders that say to get an early morning test when TSH level is highest, I have never said that's when the FT4 and FT3 is lowest because I know it isn't (and I don't think I've seen anyone else say that either). This is what I say
* Book the first appointment of the morning, or with private tests at home no later than 9am. 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.
It's the timing of the last dose of thyroid meds that affect the FT4 and FT3 levels.
This is the post showing the graphs of the daily rhythm of thyroid hormones which tattybogle has referred to:
Thank you Jazzw, tattybogle, greygoose and SeasideSusie for the speedy and informative responses (as always)! My mistake on thinking the advice about early blood draws related to T3 / T4 levels as well as TSH - I think I conflated the two in my head, so apologies for adding confusion there.
The charts are really interesting. It doesn't change anything for those of us dependent on opening hours at health centres, but it makes me wonder about trying a home test at midnight to see what difference that would make.
but it makes me wonder about trying a home test at midnight to see what difference that would make.
That's an interesting thought. I always do mine around 8.30-8.40am for consistency. I am often still up at midnight so if ever there is a 2 for 1 sale I might do that just out of interest - but seeing as my TSH always comes back between <0.005 and 0.01 (depending on lab) and the highest it got when I experimented with reducing Levo was 0.02 I might not see much of a difference. Do let us know if you ever do it
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Bit confused about blood results 
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