My Endo and the Phlebotomist have both said that my thyroid blood tests are not fasting tests but I know that this is suggested practice here.
I apologise that some of you may already have said this many times but my Endo is arguing with me and I can't find any research. I would much prefer people to speak from experience.
As you may know, my last results showed a very high (twice the top range) FT4 and a low FT3.
I took my levo at 5am and had the blood tests at 11am. No breakfast.
Can anyone advise me?
Thanks very much
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UKGirl1966
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Last dose levothyroxine should be 24 hours before test
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
Bloods should be tested as early as possible in morning before eating or drinking anything other than water
“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”
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.
I follow the fasting early morning test regimen. My first gp after diagnosis 25 yrs ago told me this and I still follow. It helps that he was the only gp I have had that seemed to have any knowledge of thyroid
Think of it as being a bit like petrol in the car. Petrol/levo goes into the tank, but does nothing there - it waits until it's needed. In the car it's used when you start the engine and drive away / in the body levo is stored as T4 and gets converted into T3 when you need it. So T4 from levo can be described as a storage hormone. That's why it's fine to leave 24 hours before the test - you can just fill up a bit later.
In one sense the Endo is right.....they don't have to be fasting , or taken after a certain number of hours from last dose, or taken at a certain time of day.......ie. the TSH/fT4/fT3 tests do work for measuring the levels (at the time) accurately whatever you do.
(As long as you don't have anything -like large doses of biotin -which could cause interference in the lab process)
However .. this issue is whether the endo is able to interpret the results correctly in the light of those conditions . And if he is not recording the relevant information , ie time of last dose /time of test... then how can he interpret results correctly ?
Time of last dose...
For example -in your case if you took last dose levo (T4) 6 hrs before test , and knowing that the peak levels after taking dose are at around 5 ? hrs after taking it . he should understand that the result he gets for fT4 will be of a temporary high point, and most of the day your level will be lower than the test result.
Time of test...
TSH has a diurnal rhythm , highest in middle of night and lowest around 2 pm, the difference can be up to 40/50%.. so in your test taken at 11 am. the result needs interpreting with the knowledge that it would have been higher at 7/8am and lower at 2/3pm.
Fasting.....
It is possible that eating breakfast may lower TSH slightly, and the reason fasting is suggested on here is because so often when new people are having trouble getting a diagnosis because their TSH is not seen as 'high enough for treatment' it is useful for them to understand how to make sure that the TSH result the GP gets is as high as it gets.
For the above reasons it is important to be consistent about your test conditions.. otherwise you can't easily compare one result with the next.
P.s i was interested to discover that vets are routinely trained to interpret T4 tests in animals in the light of the time the last dose was administered... so ask your endo to explain why something that is seen as necceasary for vets to understand before interpreting fT4 results is not seen as necessary by him.... after all wouldn't you expect an endocrinologist to understand more about this than a vet ?
Actually , i wouldn't .. i think i'd prefer to be treated by a vet !
I've mislaid the reference , but just google Hypothyroid horse / T4 test and you'll find it stated everywhere.
yes , i've heard that to , although i think it has to be "in an emergency if nothing else is available".... which still begs the question "are Gp's not trusted to treat animals even if no vet was available ?"... and if not .... what does that tell you ?
Your endo and phlebotomist are absolutely correct, there is no need to fast before a thyroid blood test. Even the team that originally 'found' that fasting affected TSH did a follow-up study showing their first study was wrong. Their statement 'TSH levels showed a statistically significant decline postprandially in comparison to fasting values' was because the postprandal blood test was hours later in the day. TSH falls during the morning!
It is good to allow at least five hours between taking levothyroxine and having the blood taken, this is because there is a small peak in fT4 (~10%) during the first few hours after ingesting the tablet. Taking your levo at 5 am and having the blood at 11 am is fine (although I wouldn't get up at 5 am!).
I advocate prior fasting (solids) for one reason. If nonfasting then presentation of each patient depends on what they have eaten beforehand. If fasting overnight then everyone is presenting in a controlled way, applicable to all. I don't like potential disrupting factors in a test - there should ld be only one variable - the thyroid levels themselves.
Whether or not eating before a thyroid blood tests affects the TSH results - and the debate will probably continue on here forever! - it is well-known that drinking coffee will lower the TSH level. So, best to avoid that.
What's more, you need to avoid as many vairables before a test as possible. So, if you were going to have your breakfast before the blood test, you would need to have exactly the same thing every time. Could you remember exactly what you had for breakfast on a certain day six weeks ago? I probably couldn't. It's easier just to have no breakfast at all.
Purely from a consistency point of view, for menstruating women it is important to have the blood taken at the same stage of the cycle ncbi.nlm.nih.gov/pmc/articl... . This has very large effects on TSH as can be seen in the bottom two graphs of Figure 1. In these cases retesting after six weeks could be the worst possible time, four or eight weeks would be preferable.
Suppose that your doctor did a thyroid function test and a cholesterol test. Fasting IS necessary for cholesterol tests, and people do get told that.
Next time the patient gets a thyroid function test (TFT), and no other tests are done at the same time, so they eat a full English breakfast with coffee before the test.
How can doctors ever know that the TFT done with fasting produces almost identical results to one with a big breakfast and coffee? They can't, because the research hasn't been done.
[There is one research paper on the subject but don't bother looking for it. It was so badly designed that the results can't be interpreted. The researchers didn't control their variables so it is impossible to know whether the differences they found were due to fasting or time of day - and we already know that time of day DOES make a difference.]
I always do my best to get tests done at around 8am - 9am, and I always fast overnight and delay breakfast, and drink only water.
...
Another link you need to know, although it is not relevant to fasting is this one ...
I think a lot of doctors have absolutely no clue what the TSH of healthy people is, so they think anything within the reference range is fine. It isn't.
The last two surgeries I have used do annual or more frequent reviews of chronic conditions diabetes/ thyroid disorders as non fasting and include cholesterol in both of these. They do come back with results indentified as non fasting.
For cholesterol only a few years ago I was asked to not fast for one and then fast for a follow up. I cannot remember why, if it was even properly explained. A good chance it was the usual vague reason given by the nurse practitioner that ‘the doctor want to see/ compare”.
Ugh! But, even with porridge, discrepencies can slip in. The water might be extra chalky that day, or something. Besides, just because no-one has proved conclusively that eating before a blood draw affects the TSH, it doesn't mean that it doesn't. And, we need as much help as we can possibly get to get diagnosed and correctly treated. If a doctor can possibly do us out of our thyroid hormone replacement, he damned-well will! And, that is a proven fact.
its all relative..... relative to how much milk is left,...how far you live away from the shop......how full the whisky bottle is... and whether anybody is looking.
I used to live in a place with no fridge , a 4 mile walk to the shop , and free whisky
We made a fabulous desert with oatmeal, raspberries, whiskey and double cream.
I was brought up on occasional porridge made with oatmeal and water, a little salt allowed but never sugar. Fortunately the breakfast routine was varied with prunes or dried figs soaked overnight to make them more palatable. Fresh fruit in season!
It's not deviating from standard guidance. I'm not aware of any guidance. What we are trying to achieve an accurate result from the blood test. In the case of patients taking levothyroxine we want to know the fT4 level. After taking levothyroxine (or NDT) fT4 results will peak for a few hours after ingestion and then follow a standard half-life ellimination curve - with a seven day half-life.
This study by Colin Dayan's team wvrtaal.files.wordpress.com... looks at patients taking at least 100 mcg levothyroxine. If you look at graph b. in Figure 1 (upper plot) you can see how fT4 varies for patients on levothyroxine monotherapy. The value varies between about 20.5 and 18.0 with a clear peak during the first five hours or so after which it drifts down from around 19.0 to 18.0. Thus, taking the blood at least five hours (and preferably before ~14 hours) will give a good indication of real average fT4 levels.
If you leave at least 24 hours you will get a wrong result - the blood test will be a waste of money. For accurate blood test results it is best to take the blood about half-way between doses, this applies to patients taking L-T4, L-T3 or NDT. It's not perfect but seems the simplest and beset method within current knowledge.
The 24 hour plus recommendation seems to have come about because somebody recommended it once and others copied it without checking the evidence. These things get passed on as fact, we need to take care before handing on information that may come from dubious sources or are just anecdotal.
Everyone, or almost everyone, coming to this website feels unwell and they have an idea, or they already know, that their thyroid might be responsible. We want to feel better. We all know that getting diagnosed with hypothyroidism in any shape or form is very difficult and can take years, maybe even decades. Doses of Levo are often too low. TSH is all that counts. Free T4 is often not even tested.
Jim lives in a different world to that of most women with a thyroid problem. After all, he got diagnosed as hypothyroid with a TSH between 1 and 2. His ideas on the appropriate conditions under which people should be tested would leave even more of us under-medicated or undiagnosed.
This argument about how and when to test gets brought out for an airing over and over again. Jim's suggestions might have merit in an ideal world. But many, many patients with thyroid problems don't live in an ideal world.
I think the testing protocol that Jim suggests might work for all of us with a compassionate and knowledgeable NHS and medical profession. But we don't have those things so we have to make the best of what we can get.
Until women with thyroid disease get treated with the same compassion as a man with thyroid disease we should always get tested under conditions that are to our advantage while also trying to keep conditions as realistic as possible.
If you want to recommend delaying a dose to push up TSH that's fine but it's important to make it clear you are doing this to give a higher TSH not to give a true result. Leaving a long gap between levothyroxine and taking the blood will have little effect on TSH but will lower fT4. Other factors such as time of month (for those it applies to), cold exposure and excercise (as well as time of day) will have a larger effect on TSH but are never mentioned.
The sad thing is most of the people I see on the forum who are doing badly have a TSH that is too low for their fT3, fT4 levels. This reduces D2 activity leading to hypothyroidism in the brain and other tissues (which cannot be measured). By trying to fiddle the blood test results they are hiding the underlying cause of their hypothyroidism and postponing the day when they will receive correct treatment.
NHS England Liothyronine guidelines July 2019 clearly state on page 13 that TSH should be between 0.4-1.5 when OPTIMALLY treated with just Levothyroxine
Note that it says test should be in morning BEFORE taking levothyroxine
If you want to recommend delaying a dose to push up TSH that's fine but it's important to make it clear you are doing this to give a higher TSH not to give a true result.
It is often mentioned on here that TSH is affected by the time of day the test is done, and that the gap between last dose and a test will affect the Free T4 (and Free T3 if relevant). So we aren't hiding any necessary information.
I don't think you have any idea how badly some women are treated by doctors. I had to wait nearly 25 years to get my first prescription for Levo and that was only supplied very reluctantly. It was about two years later when it was discovered (by accident - they were checking for something else) via an MRI that my pituitary looks very abnormal, so although I haven't actually been tested for secondary hypothyroidism I probably have it. I would never rely on a doctor to treat my thyroid ever again. And on top of that I had several low levels of nutrients usually associated with hypothyroidism that were deemed to be "fine" even though I felt a lot better when I improved them. But my experience is far from unique.
From my point of view, this forum gives members (who are mostly female) the confidence to try and help themselves, with or without their doctors approval and co-operation. It is inevitable that not everyone will succeed in optimising their health, and some people will still feel unwell. But even a 10% improvement is not to be sneezed at. We care about how we feel, whereas doctors only care about numbers. If we had the freedom to experiment and to decide for ourselves when we feel well, what dose of Levo we take, whether we take T3 or NDT, whether our nutrient levels are okay then we could possibly use your protocol for testing. But we don't, so we try and make the system (and biochemistry) work for us as best we can.
We (you and I) keep repeating this discussion/argument every few months or every year, so you are perfectly well aware of why we do things differently to you. I don't know why you want to go through this over and over again.
The sad thing is most of the people I see on the forum who are doing badly have a TSH that is too low for their fT3, fT4 levels.
That sounds interesting. Having been on this forum for about a year I haven’t read this before. In fact I keep reading : forget TSH, just look at T4/T3.
Having a low TSH myself I’ve been trying to read up on it but haven’t found anything that supports the view that a TSH between 0.4 and, say, 2 is a problem.
What ratios between TSH and thyroid hormones are beneficial and what is not good? Can you say more that can be understood by someone without Science ‘O’ level?
We're drifting off topic but in short if fT3 and fT4 are both low normal TSH should be elevated. This is why TSH can be such a good marker for early stages of primary hypothyroidism.
If you want to go into it further raise a separate post and let me know.
I was ill for about a decade before I was diagnosed. My hypothyroidism caused IBS and also gallstones requiring a cholecystectomy. The latter was delayed on good advice at the time because I suffered from bile reflux and it was thought removing the gallbladder might make this worse. Instead it resulted in considerable pain for some time. (The bile reflux ceased after I started levothyroxine - it was caused by slow metabolism). I had to give up my job and I calculated this cost me around £250,000 in terms of lost salaray and lower pension. I was very good at my job and would have expected promotion and exciting times (I worked in computing).
Being severly hypothyroid with excellent TFTs highlighted the fact that primary hypothyrodism is just one form of hypothyroidism and seeking a high TSH for diagnosis is wrong. In particular it reinforces the false belief that TSH is a good marker for thyroid status in all cases. In the long term running away from the science won't help us.
I'm not convinced of the need for a fasting early morning test despite reading the many studies but I am convinced of the need to take tests without having just taken meds -it would be crazy if they didn't skew things imho.
Thanks for these. The comments are more or less correct but could be misunderstood. For clarification the peak in fT4 starts after around two hours, some of these comments may give the impression that all is fine after two hours, that's not the case as the peak goes on for around five or six hours. Hence my recommendation to leave at least five hours between taking levothyroxine and having the blood taken.
If you take levothyroxine in the morning and the blood test is less than five hours away then it makes sense to delay that day's dose or take it the night before. What is wrong is the suggestion to 'leave at least 24 hours', leaving e.g between 30 and 40 hours will give false fT4 values and probably mess up TSH a little also. Leave at least five hours and try to keep not much above 24 hours, about 12 hours is ideal. It is wrong to recommend leaving at least 24 hours.
Getting a false low fT4 has consequences. You may be unaware your fT4 is high, with cardiac and bone risks as well as its effects on deiodinase - reduced T4 to T3 conversion and high reverse T3. It will also make your doctor think there is room to increase the levothyroxine dose rather than prescribing L-T3. We can only follow the data if we have accurate data.
No! 1. It won't work because when treated their TSH will be close to zero. 2. It will hide the fact that the problem is the low TSH be it a pituitary or other problem.
Thanks. I saw a very nice endocrinologist who said I can't be hypothyroid 'because the blood tests say so'. An old story but sad in this case because he was genuinely concerned.
I then got a private referral to Dr Gordon Skinner who diagnosed on the basis of signs and symptoms. It was then a long tactful task to get the support of my GP who did his job correctly, he was very challenging but willing to give support if we took care and presented evidence such as monitoring pulse etc. Dr Skinner's excellent book 'Diagnosis and Management of Hypothyroidism' is still avaiable. Sadly Dr Skinner died a few years ago.
Other causes of hypothyroidism include resistance to thyroid hormone (RTH) and a subnormal TSH or central hypothyroidism. I describe these on my website. We can be hypothyroid with perfectly normal blood tests either through endocrine disruption or impaired deiodinase. I've argued that it's not good enough just to see if TSH, fT3, fT4 are within their reference intervals, they are interrelated and we must look at how they interreact. This is one reason why I advocate reasonably accurate blood tests, so we can analyse the data effectively.
The problem is that the professionals have had something wrong with their training.
Our older doctors were trained before blood tests were introduced and we were diagnosed upon our clinical symptoms alone and given a trial of NDT. No blood tests were available at all.
NDT means - natural dessicated thyroid hormones given to those who were hypo and it is made from animals' thyroid glands so provide all of the hormones a healthy thyroid gland would contain.
So through lies and persuasions the announcement was that NDT was not consistent whilst not informing us that when it was first diagnosed there were no blood tests alone - we were diagnosed solely upon our clinical symptoms alone and given a trial of NDT, slowly increased until symptoms resolved.
We advise to get the earliest possible blood tests, fasting (you can drink water) but we must have last taken a dose of thyroid hormones, 24 hours before the blood test. Taking it later in the day will give false numbers.
The Endos etc are arguing with you because that is what they 'assume' but we, the patients, know better because we have the actual hypothyroidism.
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Fasting or non F Blood Test
Why is fasting important before a blood test?
Fasting blood test
Fasting before a blood test?
Does TSH blood test have to be a 'fasting' blood test please? 
