Time of TSH blood tests

[Lilly12255]

Has anyone compared if TSH test come out higher early morning (8-9am) or later in the day? Lunch time, afternoon

[Horsey07]

I’m going to do exactly that this week. I had general blood tests done after lunch two weeks ago. I now have a Blue Horizon kit and intend to draw blood early on Tuesday morning, fasting. I’ll let you know if it makes a difference.

[SlowDragon Administrator]

TSH has significantly diurnal variation

healthunlocked.com/thyroidu...

So it’s important when you test TSH ....

researchgate.net/publicatio...

“According to the current TSH reference interval, hypothyroidism was not diagnosed in about 50% of the cases in the afternoon.”

“Further analysis demonstrated inadequate compensation of hypothyroidism, which was defined in 45.5% of the morning samples and in 9% of the afternoon samples”

ncbi.nlm.nih.gov/pubmed/252...

TSH levels showed a statistically significant decline postprandially in comparison to fasting values. This may have clinical implications in the diagnosis and management of hypothyroidism, especially SCH.

Median TSH graph

healthunlocked.com/thyroidu...

[Lilly12255 in reply to SlowDragon]

So if I understand correctly, testing early in the morning will give the highest TSH blood test result?

[greygoose in reply to Lilly12255]

The highest would be around midnight, but we can't test then. If we rely on NHS labs, the best we can probably do is around 8.30 am. But, aim for at least before 9 am. And avoid 12 noon, because that's when it's at its lowest.

[SlowDragon Administrator in reply to Lilly12255]

Testing before eating or drinking anything other than water

And last dose levothyroxine 24 hours before test

[Lilly12255 in reply to SlowDragon]

Thanks for posting these articles. Looking at the graph on the first article, it looks like TSH decreases in the morning until 8am and then has a small peak at 9am before declining again. However, other graphs in the same article suggest that it decreases straight. Can I check with you if I understood correctly that the optimum time for maximising the TSH test is 9am?

TSH

[SlowDragon Administrator in reply to Lilly12255]

It’s at its highest in middle of night…..obviously can test then

If testing privately, many test early morning (6am-7am) and should aim to test before eating or drinking anything other than water

If testing via phlebotomist usually earliest appointment is 9am, but some clinics open at 8am

[Lilly12255 in reply to SlowDragon]

It's NHS. I can book appointments anytime from 8:30am. Looks like 9am in the peak rather than 8:30am, is that correct?

[helvella Administrator Thyroid UK in reply to Lilly12255]

No - I think you are taking one graph of one set of results and assuming it applies to you.

Your personal TSH might not have the somewhat odd small jump, or its timing might not be 9:00 rather than 8:30.

Have a look at this paper:

academic.oup.com/jcem/artic...

It has more charts/graphs which show how TSH patterns can vary between individuals.

The point of these graphs is primarily to show that TSH not only varies, but that the variations can be very significant. They imply that you should probably avoid late morning/afternoon tests. But the only way to be absolutely sure, for you, would be do do multiple tests - maybe every hour? Obviously hopelessly unrealistic. Without that you are into best-guess mode - but don't take precise patterns as being accurate for you.

Just think of three people who are very, very similar. But one goes to bed at 22:00, rises at 06:00, second at 23:00 rising at 07:00 and the third 24:00 to 08:00. If TSH is even partially related to sleep cycles, you can see why their TSH tests might not align.

[Lilly12255 in reply to helvella]

Am I right to think that I would be better off doing TSH as early as possible and then go back to hospital to do the FT3 at 3pm in the afternoon?

[helvella Administrator Thyroid UK in reply to Lilly12255]

Afraid that is, simply, unrealistic.

You will almost certainly not get any doctor or lab to agree to that. It is usual to do all the tests on the one draw of blood.

And, so often, FT3 (and FT4) doesn't get done at all.

Target getting TSH done earlier. FT3 doesn't usually vary that much.

[tattybogle]

in theory, it will make less difference once someone is treated with thyroid hormone replacement. ..... taking exogenous hormones usually blunts the duirnal rythm to some degree, but it seems wise to still follow the 'early morning =highest/1-3pm =lowest' protocol, even when taking thyroid hormone replacement, or at least keeping time of test consistent., as there is still a difference .. even though it's a smaller one.

Maybe it's blunted because of the timing and taking of dose all in one go instead of the natural pulsatile release from thyroid gland. So it is most useful for diagnosis, before treatment has started ie. 9am might be high enough for TSH to be over-range , but 2 pm might not be.

Sorry i can't remember where i filed the study that showed it was blunted.. but am sure i read it somewhere.

[shaws Administrator]

TSH is always higher early a.m. and drops throughout the day.