Thyroid UK

Blood test timings

I was interested to see that it is best to test early am as levels peak around 3am? The last test I had was done early evening at the docs and my TSH was 2.7 - I have watched my results climb steadily over the last 2 yrs from 1.3 to 2.29 and now 2.7.

I await my recent results for the T3 and pituitory gland with bated breath. These the Endo did for me.

Juts a thought here - if my TSH was 2.7 at that time of day would it have possibly been higher if the bloods had been drawn at say 9am instead that day.??

Thanks again.

3 Replies

Someone else has asked a similar question to this so I have asked our Advisory Panel. I'll get back to you when they respond.


There is quite an interesting paper on the way fT3, fT4 and TSH vary through the day - happily it is freely available as a PDF here:

(Even if you only look at the graphs it is illuminating.)

For those already being treated, the abstract below is also interesting. Unfortunately the full paper is not available for free. It expressly suggests that test results might be in range some of the day and out of range at other times.

Diurnal variation in TSH and free thyroid hormones in patients on thyroxine replacement.

Sturgess I, Thomas SH, Pennell DJ, Mitchell D, Croft DN.

Department of Nuclear Medicine, St Thomas' Hospital, London, UK.


Eleven patients with treated hypothyroidism were investigated to examine the effects of time on their thyroid function tests. Each patient was clinically and biochemically euthyroid on once daily thyroxine replacement therapy, taken in the morning. TSH followed a diurnal rhythm with a peak level at 23.30 h and a trough level at 14.30 h. Four subjects had TSH trough levels within the normal range, but with peak levels outside this range. FT4 and FT3 levels fell from their highest levels some three hours after ingestion to the lowest levels just prior to the next dose. This study shows that there are significant time-related variabilities in TSH and thyroid hormone levels in treated hypothyroid patients. This should be taken into account when interpreting results of their thyroid function tests.



Hi Stacey, One of our advisers has just come back with this answer:

"Diurnal differences in TSH are likely to be marginal. A reading above 2.5 in a subject not on treatment with thyroid hormone is nowadays officially considered compatible with hypothyroidism.

In patients on treatment a corresponding level may indicate undersupplementation."

We must bear in mind though, that this doctor is from Sweden and people there, as in the US, get treated once their TSH reaches 2.5.


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