Hi, just need some advice on doing Thyroid blood tests in the evening. I have seen the protocol for doing it in the morning before 9am and on an empty stomach etc.
What about if your taking your T4 medication before bedtime at 11pm after eating your last meal 4 hours before. Do you take your blood test at 11pm before medication to get an accurate result? Is that recommended?
No
TSH is highest early morning and is all most medics look at
We always recommend testing early morning, ideally before 9am, only drinking water between waking and test and last dose levothyroxine 24 hours before test
So
If you normally take levothyroxine at bedtime/in night ...adjust timings as follows prior to blood test
If testing Monday morning, delay Saturday evening dose levothyroxine until Sunday morning. Delay Sunday evening dose levothyroxine until after blood test on Monday morning. Take Monday evening dose levothyroxine as per normal
You can take the blood at 11 pm if you want to. You can also take it in the morning or during the day. The recommendation to fast is very dubious, studies of TSH throughout the day do not show it jumping around at mealtimes!TSH is lower in the middle of the day which may be a hindrance if you needed more hormone. On the other hand TSH is level during the day and so results will be more consistent. Make sure you don't take the blood within four hours of taking your hormone tablets. About half way between doses is ideal.
super1, Whatever you decide to do about the time you do your own blood test, consistency is important, so that a direct comparison can be made with each previous test. Whilst you could theoretically take your own blood at 11pm, that would not be consistent with a blood draw done through the NHS / private medical practise etc., as it outside normal working hours. This would mean your own 'at home' test could show very different results, so comparison from one test to the next would not be possible.
The results at 11 pm are almost identical to those at 8 or 9 am academic.oup.com/view-large... .
Interesting, thanks 😊 Is that graph for 'normal' people (i.e. no thyroid dysfunction), or specifically for those on exogenous thyroid medication?
It's from this study of healthy individuals academic.oup.com/jcem/artic... . They had standard meals at 08:30, 22:30 and 18:00.
Hiya Jim
I have this information on my local Devon Group which now has 351 members. Its also on Hypothyroidism Support UK and Thyroid Health Support UK both of which I admin on.
Some useful info for those of you having blood tests done and how to get the most from them:
How to get accurate Blood Test Results put together by a friend Katharine Margaret North:
We often have members posting that they’re feeling symptomatic, yet when they have their blood tests, their results are always within range, so the doctor won’t increase the medication, even though the patient is symptomatic.
There are several reasons why this might happen, but one very common one is the timing and conditions of the blood test.
For the most accurate thyroid test results, you need to have your blood test early in the morning (before 9am), fasting from midnight (water only), and wait to take your medication until after the blood test.
If you’re taking any vitamin b complex supplements containing biotin (b7) they need to be stopped 7 days before the test.
TSH fluctuates diurnally. It’s highest during the night and lowest in the afternoon. Eating/drinking also lowers TSH. Tests carried out later in the day can lead to misdiagnosis and if on medication can cause dosage to be adjusted unnecessarily.
Tests carried out at different times during the day are not comparable. You should always have your tests at the same time.
researchgate.net/publicatio...
biomedpharmajournal.org/dow...
pubmed.ncbi.nlm.nih.gov/258...
pubmed.ncbi.nlm.nih.gov/716...
ncbi.nlm.nih.gov/pmc/articl...
verywellhealth.com/optimum-...
There should be a 24 hour gap between your last dose of levothyroxine and the test. Tests done after taking medication are measuring your last dose before it leaves the bloodstream, in addition to your normal average blood level.
Levothyroxine spikes in your bloodstream 2-4 hours after you take it and takes several hours to be absorbed.
These links explain it very well:
theinvisiblehypothyroidism....
thyroidpharmacist.com/artic...
These are patient to patient tips. Doctors generally will not listen when we try to explain this to them.
Janexxx😊❤️
Hi Jane,
The diurnal fluctuation in TSH is well established. "Most accurate test results" is a confusing concept. In practice the most accurate result would be obtained in the middle of the day when TSH remains around its lowest point, the curve is flat and so it is easy to compare one test with another. Early morning the curve is on an upward slope and consequently results will fluctuate depending on where the body clock is on the particular day. However, most studies will take the blood early morning so this will be the most useful and representative time (with the caveat that TSH isn't a particularly good marker except when it is very high - treat the patient not the numbers).
I disagree with the general consensus that fasting has a significant effect on TSH. I'm very familar with the Indian study you reference. Unfortunately, the Indian study was useless, they took blood at 7:30 and then at 10:30. Of course TSH was lower, having breakfast was irrelevant. A couple of years later they did a half-decent follow-up study ncbi.nlm.nih.gov/pmc/articl... which showed that the fall in TSH was due to timing not fasting. I've seen some other studies which failed to find a link between fasting and TSH.
There are a number of studies of Ramadan fasting with variable results, I don't think these are relevant because it involves long term fasting and altered sleep / eating habits.
A chinese study ncbi.nlm.nih.gov/pmc/articl... does appear to show that eating lowers TSH. However, I am suspicious of this study because it is known that many Chinese "studies" are ghost written to order (doctors in China have to publish many studies to get promotion) and most importantly this study achieved remarkable levels of significance (p<0.001) whereas other studies failed to find any significance.
Another way of looking at it is observing studies of 24 hour TSH levels, we don't see a drop in TSH after meal times.
I appreciate doctors are fixated on TSH and told they should only diagnose if TSH > 10.0 (and fT4 below the lower reference point). Trying to get your TSH just above 10.0 (or 5.0 if the doctor is more reasonable) is an understandable objective. Even if you achieve a higher TSH it has two drawbacks. 1. It reinforces unreasonable faith in TSH as an accurate marker of thyroid status, harming patients in the long run. 2. If you have a degree of central hypothyroidism you are shooting yourself in the foot.
More important than the diurnal variation in TSH is the effect of the menstrual cycle. It will apply to a minority of hypothyroid patients but the phase of the cycle can have a large effect on TSH. See the bottom two graphs in Figure 1 of this study doi.org/10.3389%2Ffendo.201... . In view of this the practice of testing TSH every six weeks is asking for trouble as someone might occilate between the beginning and middle of their cycle giving very confusing results! Young women seeking a primary hypothyroidism diagnosis would be better advised to have a healthy breakfast and book the blood test mid-cycle.
As your friend noted you shouldn't have the blood taken within four hours of taking any thyroid hormone.
Hi Jane,
Great advice and references.
Last year I too put together a post re test timings that also includes T3 and NDT that your members might find useful …. healthunlocked.com/thyroidu...
Thanks for your comments. Interesting, on the last 2 occasions. My results were as follows.
First time. Took Levo 125mcg at 11pm Sunday night and tested next day. 9.5 hours gap. Monday morning at 8:30am after waking.
TSH - 1.6 (normal range 0.27 - 4.2 mU/L)
T4 - 24.1 (normal range 12 - 22 pmol/L)
T3 - 3.5 (normal range 3.1 - 6.8 pmol/L)
A week later. Took blood test at 11pm before medication. So a 24 hour gap and about 5 hours after last meal.
TSH 0.87 (normal range 0.27 - 4.2 mU/L)
T4 - 20.7 (normal range 12 - 22 pmol/L)
T3 - 3.6 (normal range 3.1 - 6.8 pmol/L)
My vitamin levels are all good.
Vitamin D = 88
Folate = 14
Active B12 = 107 pmol/l
Ferritin = 136 ug/l
Haemoglobin = 145 g/l
Transferrin saturation = 45%
So your TSH is noticeably lower testing in evening compared to morning
Ft3 unchanged
Ft4 over range when tested after 9.5 hours
Ft4 at good level when tested 24 hours
which exactly demonstrates why we say
Test early morning and last dose levothyroxine 24 hours before test
Please see my response to Jim. 😊❤️
Thyroid Blood Test Results
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