Just sat reading the "UK Guidelines for the Use of Thyroid Function Tests" as formulated by the Association for Clinical Biochemistry (ACB), the British Thyroid Association (BTA) and the British Thyroid Foundation (BTF)…..I really should get out more often.
Pondering the whole TSH as a measure of thyroid function controversy, I was interested to see that the guidelines do acknowledge that “the secretion of TSH is pulsatile [brilliant word – means beating rhythmically!.... by that I think they mean it has a circadian rhythm] and night time concentrations are higher than during the day”. I did in fact know that already and recently read elsewhere that there is a 72% variation between your night-time TSH and that during the afternoon.
If this is the case, not only does it have important implications for when we as thyroid patients go for our blood tested (I always fix my appointment first thing in the morning). More importantly, however, are the implications of this for the labs when testing subjects to determine reference ranges. The guidelines go on to state that:
“For TSH, reference ranges should be established using specimens collected between 0800h and 1800h”,
- which is quite a wide window of time considering its “pulsatile” nature (I am going to try and use that word at least twice daily this week!). Surely collection times, at the very least, should be standardised between labs???? It raises all sorts of questions like do they take the blood samples to establish their reference ranges at staggered intervals during the day to compensate for its “pulsatile” nature (.....doing well!) or do they simply call their subjects in all at the same time?
Am I missing something? As far as I can see, this state of affairs could potentially result is quite a variance between different labs. Are you out there Helvella, Diogenes….PR4NOW…. and the like….have you any thoughts on this? Considering it’s pulsatile nature (hat-trick!) and the wide range of its variation and the fact that we are dealing with tiny hormonal shifts correlating with symptoms I would have thought it was of paramount importance to have this more closely pinned down.
Thoughts/observations/corrections much appreciated.
Written by
MacG
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Whatever was done when the first TSH test was developed is entirely irrelevant now. There has been acknowledgement of the need to exclude anyone with a thyroid issue. Tests, at least mostly, now manage to avoid producing high TSH results due to macro-TSH (an antibody to TSH itself attaching to a molecule of TSH). Test ranges have been established and tweaked by manufacturers and laboratories around the world.
It still isn't either a perfect test in itself, nor an adequate assessment of thyroid status on its own. It can, sometimes, be a useful tool.
The pulsatile nature seems to be more subtle than one squirt a day. The difference between maximum and minimum does vary between people with some showing virtually no variation, others a substantial change. See my year-old post and the previous one that refers to!
The difference between 08:00 and 18:00 can be very significant. One paper expressly drew attention to that issue and suggested that for borderline cases, it could easily make the difference between diagnosis and being ignored or put onto wait and watch.
Ironically, the TSH will still be varying when a person is on levothyroxine full replacement. Not as fluctuant but the circadian rhythm apparently just won't stop even though blood levels of hormone are not fluctuating much at all when taking Levo.
So, don't know. If someone is not taking anything at all, then clearly getting blood taken first thing in the morning is a wise move for diagnostic purposes. If a person suspects that their dose is too low, then getting TSH done early is also a good move. That's valid for primary hypothyroidism.
The problem happens with secondary hypothyroidism because the TSH is always in low range regardless of fT4 and fT3.
There are many problems with the TFTs and since allopathic doctors do not seem to understand any of them, this then becomes a problem for the patients. Calling the reference range the normal range is a complete misnomer and implies a degree of accuracy that the tests cannot support. The debate over the reference range, the lack of a universal standard, (now being worked on), the lag time of the TSH in regard to the clinical presentation of symptoms, the work of Drs. Hoermann, Midgley and Dietrich on the standard model are but a few examples. In reality the circadian rhythm, although a problem, is but a minor one. PR
I read somewhere that the 'clinical tests' involving TSH consisted of a group of 12 people! Levo has NEVER had any clinical tests and the TSH bloods were invented to support the use of levo as I read it.
Measuring TSH as a standalone test is a basic affront to science. I could make a day's comment here as regards its length and obliterate the site, but put simply, we've got a) inconsistency in TSH measurement by individual manufacturer's tests (around 20% lowest-highest) b) TSH is two removes from FT3 which is the determinant of metabolic health (T4 being the thyroid-produced intermediate) c) FT3 has a very small rhythm that follows closely the much bigger TSH daily rhythm, d) the reference range for TSH depends on your weight, age, size of thyroid, and whether you are on T4 or not. The paradigm has to move from the statistical catchall diagnosis (are you within the goalposts or not - which themselves are shadowy, not fixed) to a personal appraisal of the individual. I've had to learn this the hard way from simple evidence that shows lumping together everyone, getting a range and using that as a yardstick diagnosis for the individual simply won't fly any longer. And all the work we're doing puts more and more nails into the catchall coffin.
Thanks so much for chipping in Diogenes. What you are saying here at the end of your post about the personal appraisal of the individual relates to the paper by Hoermann, Midgley et al. (Homeostatic equilibria.......) right? In a note to Thyroid UK John Midgley said "Just thought you'd like to know that the avalanche is beginning." Is it??? I wonder how far away more personalised testing is.
Congratulations MacG on your hat trick! I can't add anything constructive, but I am forever impressed by people on this site who frequently know so much more than their doctors do about thyroid hormones. When will our doctors follow our lead and swot up on the subject if they don't understand it (since they feel so free to tamper with our vital hormones)?
Ah Dolphin5! I failed miserably today in my quest to use the word "pulsatile". However, I teach music in a sixth form and the students are back later this week.......!!
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New paper on TSH and FT4 reference ranges
