Best time for blood tests?

[Macey2009]

Hi I have seen a few posts recently that it's best to have bloods done at 9am.

All my previous bloods have been 8.10-8.20

As I was read on here the earlier the better.

Is it worthwhile changing the time next bloods or just keep the same time?

[greygoose]

I'm not sure 9 am is actually the best time. But it's often the most practical. I would say that if you can continue to have your blood draw between 8.10 and 8.20, then do so. Consistancy is the most important thing - as long as it's before 9 am.

[SeasideSusie Remembering]

Macey2009

Here is a graph of the circadian rhythm of TSH, you will see that TSH is highest between approx midnight and 4am then lowers, the lowest point of early morning time seems to be just after 8am then it gradually rises to the next highest time at 9am. It is the circadian rhythm of a healthy thyroid, when on thyroid meds one never knows so we have to decide what time we want to test then stick to it to be able to compare results.

TSH

[HEA72 in reply to SeasideSusie]

Just a thought, what happens when we change to BST from GMT? Do our body clocks/circadian rhythms stay at GMT? Otherwise being an hour out with the clock change could make a difference to when to get bloods drawn. 🤔

[SeasideSusie Remembering in reply to HEA72]

For two days a year I don't think it's worth worrying about, just don't make an appointment for a blood test on the day we change the clocks.

[HEA72 in reply to SeasideSusie]

What I meant is, do our body clocks stay at GMT or move to BST? Because if our actual body clock stays at GMT in BST time, then we'd need to adjust the time we have the bloods drawn to get the peak of TSH. So e.g. 9am GMT TSH peaks but in BST would that be 10am if our body clock remains at GMT? 🤔 I know in Chinese medicine, they say the meridian system/organ clock stays on GMT even when we switch to BST.

Sorry if this is making it complicated. I just have an inquisitive mind 😄

[SeasideSusie Remembering in reply to HEA72]

I wouldn't have a clue, and not something that worrries me considering that TSH isn't a particularly helpful test once diagnosed and on thyroid hormone replacement, FT4 and FT3 are the important tests.

It's possibly a question for a scientist or someone far more clever than me. Maybe diogenes can help.

[diogenes Remembering in reply to SeasideSusie]

This paper discusses chronolgical effects on TSH.

Life

PMCID: PMC8151474PMID: 34068480

Chronothyroidology: Chronobiological Aspects in Thyroid Function and Diseases

Giuseppe Bellastella, Maria Ida Maiorino, Lorenzo Scappaticcio, Annamaria De Bellis, Silvia Mercadante, Katherine Esposito, and  Antonio Bellastella

[tattybogle in reply to HEA72]

circadian rhythm alters by the time of sunrise /daylight length/ nightime length temperature etc etc .. not abstract /manmade issues like clocks and what time we decide to say it is. it doesn't know that we put the clocks forward, or back . It is neither at BST or GMT

.. spring , summer, autumn, or winter is probably about as accurate as the body clock gets , and if you hop on plane to the other side of the atlantic it will be a bit behind ,, (or in front depending which way you went ) for a few days/ weeks untill it figures out that 'the dark has moved' , if you flew to the arctic it would presumably take it a while to figure out that 'winter appears to have come early this year' , moving the clock an hour probably has very little effect on it.

Don't put too much store by there being this little peak at 9 am tha you are trying to catch ~ that graph was from a study of 33 people , and it 'appeared' to show a little blip at 9 am,, but we don't know if that was BST . or GMT or winter or summer and when we take into account the pulsatile release of TSH , the chances of 'everybody' having a slightly higher TSH at 9 than 8. 30 are very slim indeed .

Just do whatever you do as consistently as possible. (unless you can find someone to pay to test your TSH every 45 minute over a 24 hr period (several times) then you will know what YOUR TSH does.)

9am is merely a 'best guess' about when it is likely to be highest , thats all.....it's not an exact science .

[HEA72 in reply to tattybogle]

Hi tattybogle

That's really interesting and helpful, thank you for your informative answer 🙂

[Macey2009 in reply to SeasideSusie]

Thanks for the reply. I've had i think 6 NHS tests now at around 8.10-8.20 for consistency. So actually 9am would have been better to get the highest TSH?

I wish i knew that 😣

[Dalias in reply to SeasideSusie]

Thank you for this information. So if I have a blood test let's say at 8.30am should I still take my meds when I get up let's say 7am? or should I wait after the blood test? Thank you.

[Venicefan in reply to Dalias]

you should always wait until after the test to take your levothyroxine. If you take it before the test you’ll get a false high t4 result.

You need a 24 hour gap between the last dose of levo and the test to get an accurate t4.

[SeasideSusie Remembering in reply to Dalias]

Dalias

This is the advice we offer members when having thyroid tests:

* 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.

In fact, 9am is the perfect time, see first graph here, it shows TSH is highest around midnight - 4am (when we can't get a blood draw), then lowers, next high is at 9am then lowers before it starts it's climb again about 9pm:

healthunlocked.com/thyroidu...

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.

* Nothing to eat or drink except water before the test - have your evening meal/supper as normal the night before but delay breakfast on the day of the test and drink water only until after the blood draw. Certain foods may lower TSH, caffeine containing drinks affect TSH.

* If taking thyroid hormone replacement, last dose of Levo should be 24 hours before blood draw. If taking NDT or T3 then last dose should be 8-12 hours before blood draw, split dose into 2 or 3 and adjust timing the day before if necessary. This avoids measuring hormone levels at their peak after ingestion of hormone replacement. Take your thyroid meds after the blood draw. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results.

* If you take Biotin or a B Complex containing Biotin (B7), leave this off for 3-7 days before any blood test. This is because if Biotin is used in the testing procedure it can give false results (most labs use biotin).

These are patient to patient tips which we don't discuss with phlebotomists or doctors.

[Dalias in reply to SeasideSusie]

Thank you very much. I did not know that and neither the GP nor the consultant had told me this. I will apply your recommendations on my next blood test.

Best regards

[tattybogle]

This paper may help.. (well, it's pictures might) frontiersin.org/articles/10... "Within-Person Variation in Serum Thyrotropin Concentrations: Main Sources, Potential Underlying Biological Mechanisms, and Clinical Implications"

due to the pulsatile nature of TSH secretion, it is impossible to know whether you as an individual would actually get a higher result at 8.30 or 9am,.

The best we can do is to understand the basic principle of the how TSH secretion works with the circadian rhythm, Highest 2- 4 am (ish) .. gradually falling to lowest 1-3 pm (ish) and be as consistent with test as possible ,, while accepting that mini 'pulses' do occur every ?45 minutes (ish) and whether we test at the peak of one of these mini pulses, or in-between then , is entirely up to chance.

mini pulses of TSH

[HEA72 in reply to tattybogle]

I wonder if TSH influences the adrenal glands? Because I feel more tired at 1-3pm (like my battery's running low) but will often wake at 2-4am (feeling the stimulus of higher cortisol). I'm hypothyroid.

[tattybogle in reply to HEA72]

yes im sure they are all linked to circadian rhythm ,, but cortisol is above my pay grade (and largely beyond my understanding) . As for BST/GMT.. we don't have any information about when these studies we have graphs for were done .. BST or GMT.. so ...it's anybody' s guess.