In another post earlier today, there was a discussion about two TSH results being quite different due to being tested at different times of the morning.
Surely as long as you test at a consistent time of day, before 9.30ish, the results are comparable??
Does testing 2-3 hours before 9am make that much of a difference?
Would there be a similar difference with T3 and T4 results? And for that matter any other test done between 6 -9am?
If there is a difference due to timings, I've been doing tests wrong for over a year. So all my results might not be a true reflection of my thyroid health! That worries me as I'm on thyroxine.
Also, Is there a recognised general pattern of TSH and Thyroid hormone levels throughout the day??
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Kit_Monster
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I'm not sure which discussion you are refering to but I'll post you a couple of graphs for TSH and T3. Not sure if you mean if you take T3 or general population.
Thanks Jaydee. This shows that on the general population, there's quite a difference in TSH at 06:00 and 09:00.
And shows the uptake of T3 meds really well too... And it's triggered a little lightbulb moment - as the half life of T3 is shorter than T4, that's the reason for taking a split dose for NDT or T3. 💡 Don't know why that didn't register before; makes total sense now.
Yes, which is why we say 9am is where to aim for appointment & waiting time slots permitting. When GPs dose people by their TSH it's really important to catch it as high as possible.
Hi Rachel20, thanks for replying. I knew I'd read your post but couldn't flipping well find it to reference it when I wrote mine. Yours set my brain whirring!!
Ha ha yes delightful to hear it sent someone elses brain whirrling Confused is the word.I doubled check exactly when i took the first test from my notes and it was at 7.30 with monitor my health and had Tsh 4.73 and my second 2 weeks later with medichecks at 8.20 and got Tsh 2.73 So was baffled by the huge discrepency.Did not think that just 50 minutes could make such a difference.I went from being told i have mild underactive thyroid to being absolutley fine within a week an a half taking time for tests to get there taken out.Oh dear, well i dont feel fine whatsoever but thank goodness i have a sense of humour.x
Your point about results being comparable makes sense. If you were monitoring for yourself, only, it might not be much of an issue.
But the other people who see your results, your GP, endo, or whoever, will look at the numbers without considering time of day.
Even if they tried to allow for time of day, they can't. The pattern of TSH change by time varies with some having massive variation and others very little. Unless you have gone through the sort of sequential testing referred to in other answers, you really don't have anything to base adjustments on.
If you and another person turn up, maybe your result is 1.0 and theirs is 2.0, they will simply assume you are OK and the other person needs a bit more levothyroxine. But a difference at that scale could be due mostly (or partly) to time of blood draws.
I always have blood taken early afternoon when TSH levels are stable. Early morning results will be inconsistent as you are measuring TSH during the steep slope. If you get up early for a blood test you will simply shift your body clock.The TSH rhythm reflects a reduction in TSH bioactivity overnight resulting in a need for more TSH to produce similar T3, T4 levels. For patients on full doses of exogenous thyroid hormone this diurnal fluctuation is unlikely, especially if the thyroid is caput. A formal study is needed to confirm.
note ... each person is going to be a bit different in reality ,the graphs you see are either showing samples from a few people in a study.. or they are sometimes one individuals actual levels... but in order to know what YOUR TSH does , you would have to test your TSH every eg. 45 minutes in controlled conditions for a 24 hour period .. ie in a research setting.
So the best any of us can do is hope we are 'something like' these graphs.. we may have much less movement each day than they show .. or we may have more.. and the precise times of the highest and lowest , and of little mini peaks will be a bit different for all of us .
The chart semanticscholar.org/paper/F... shows that TSH levels off between 10:00 and 20:00 hours. It will be different from day to day, it is a relative effect. (note that the variation in fT3 is actually quite small, the graph has been enlarged).
TSH is a pulsatile hormone, it is not steadily secreted as can be seen in Model 4 of this diagram from a study by Thyroid UK advisors researchgate.net/figure/Pul... .
You can see better in this model how pulses of TSH secretion contribute to fluctuation in TSH levels frontiersin.org/files/Artic... .
TSH changes throughout the day, with exercise or cold exposure and to a greater extent during the menstrual cycle. The assays are also a little imprecise, the same sample measured twice in the same machine may give results a few percent apart. We shouldn't get too hung up about minor variations in TSH.
Very interesting, the first well conducted study I’ve seen that finds an effect of food / calories on TSH. It may be because the subjects were sick people but many hypothyroid people also have illnesses if only because they tend to be in an older age group.
I used to work in Health Care for older people. Got very annoyed when the poor elderly patients had strokes and were on 25mcg levo and TSH of 7 with no testing of FT4 and FT3 of course. At peast half a page of BP drugs for other illnesses which they may not have needed had they been dosed properly or may be even some T3 added, used to mutter alot under my breath as not allowed to say anything 🤔 Just because older people's TSH rises with agee, dpesnt mean they shouldnt be treated?
Would be interesting to know how many patients in nursing homes have low dose levo or are left without treatment who might even
have remained independent had they been treated properly?😒🤓❤
If anyone needing a TSH test also has one of these tests, they will be fasting. But they might, or might not, have been fasting on previous or later blood draws.
Had it been proved that fasting makes no difference at all, that’s fine. But even if it makes a small difference, such as 5%, that could both have been missed because it is small and yet have enough impact on test results and their interpretation to have significance.
It takes this sort of research to identify the impact of fasting. Not casual “looks much the same so has no impact” assessment.
And, without proof, I have long suggested that the only safe approach is to assume that fasting has some, albeit it possibly small, effect and therefore always to fast.
This now seems to confirm that a precautionary “always fast” approach was sensible.
Nice find Jane ,, This is pretty conclusive evidence if you ask me ..... i shall stop telling people that "the only evidence for breakfast reducing TSH is shonky"
So basically if you eat 300/400 calories of 'anything' for breakfast at 7am your TSH could be anything from approx 15% -30% lower by 9 am
Where as if you don't have any breakfast it would only be 1.5% - 5% lower by 9am .
if i'm reading it correctly ( which i'm not totaly sure i am) .. it looked like the higher the TSH was to start with .. the bigger the reduction was ?..( meaning 'breakfast' is even more of a disadvantage for undiagnosed people with eg TSH 5/6 than it is for people with eg TSH 2.5 /3.5.. thereby disadvantaging the very group of people the TSH test is supposed to help most )
More proof that the NHS should be doing TSH testing consistently in the early am and before breakfast is eaten.
I think i will add this paper to my pinned post that list of recommendations for GP's to keep TSH between 0.4 /0.5 and 2/ 2.5 .. so people can use it to counter GP's saying time of test/ fasting is not relevant .
In days past, I used to get my blood drawn at the phlebotomy unit of the local hospital. Without appointment.
Time per patient was tiny. I think it took them longer to write the label than do the draw!
Nowadays, have to contact GP surgery, make appointment, and the blood draw process takes several times as long. (Not criticising the person who does it - but the need to be called, go in, pleasantries, etc. just take longer!)
Minimising time enables more blood draws per hour. Therefore potentially supports more early draws.
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Effect of exercise on thyroid blood tests?
Confused 🤔 
Private blood testing.
Latest thyroid results after splitting dose the day before - NDT
