Thyroid UK
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On blood tests in general and TSH test in particular

Hi there!

In case this is of interest… here are a few links about blood tests in general and thyroid tests in particular

Extract of the above article below, however I found the article as a whole interesting to read:

"Laboratories always indicate, for every requested parameter, a range of reference values. The norms are defined to include 95% of the "healthy" population within this reference range, with 2.5% of subjects above and 2.5% under the proposed range. It is simply a general rule!

… An excellent example of the inadequacy of relying on the reference values can be seen with Thyroid Stimulating Hormone (TSH)… A longstanding controversy with the standard ranges concerns the upper limit of references ranges for TSH, classically defined between 4 and 5. It now seems likely that the sample Caucasian population that was used to establish the "healthy" range of TSH was actually significantly "contaminated" by subjects with low-grade thyroid disease…

By introducing into the sample reference population a significant proportion of subjects who were slightly hypothyroid… the reference values were thus biased. Since then, calculations performed on a population pre-selected by a blood test and screened for auto-antibody carriers, and an ultrasound of the thyroid gland to detect goitre, resulted in quite different values. These results suggest that the upper limit for TSH should be brought down to 2.5 instead of the 4.5, which is still used to this day by most laboratories…"

And in the UK GPs won't diagnose hypothyroidism unless TSH comes up above 10...

Another link about what a joke blood tests can become depending on how they are used and what population the “normal ranges” are based on:

And another link. This Dr explains how hard it is for a Hashimoto patient to be diagnosed on the basis of “the TSH test”… it just makes no sense whatsoever:

5 Replies

Thank you for this.

It is my long held belief that the only true measure of thyroid status is through assessing symptoms. Why doctors cling to the use of TSH values is beyond me. Certainly some sufferers will be picked up using whatever values are currently the vogue, but my belief is that there are many, many more who are being missed. I have no scientific research to back that up, only a large number of people to whom I've spoken over the years, who have suspected a thyroid problem because of their vast array of symptoms (often completely debilitating) only to have their suspicions dashed by their GP.

Jane x x


yes, I had this experience yesterday with my GP. He thinks since I don't have a thyroid any longer it isn't necessary to measure Ft3, Ft4, T3, T4 etc. I asked him well how will you know if the Synthroid 50mcg, and especially the Cytomel 15mcg is the right dosage? He said that TSH testing will determine that since I don't have a thyroid anymore. It isn't necessary to know the other values just to know the TSH!!


Pleased you posted this - thanks.

If you look at this it's possible to make a rough guess, based on healthy young people, that the top of the range for TSH is 2.3 mU/L and 1.4 mU/l and T4 between 17 & 16 pmol/L. This takes into account the circadian high and low and if you take normal day time, the time when folks get the blood taken, the range is very small indeed for healthy people.

In your last video link the Doc states that T4 is the feedback signal for the production of TSH - the above paper suggests there is no link between T4 production and TSH, however there is a link between TSH and T3 production.

I have asked, in a precious posting, of those on the forum who take T3 only and no T4 just what their TSH levels where - the answer - very very low or zero. I was interested you see. Seems to confirm that low T4 does not stimulate TSH production.

The above paper does not say just what kicks off the circadian rythem for THS and T3 - just there is one. So if you feel HyptoT and the Doc is not responding to your feelings you have a chance of getting highish TSH and lowish T4 to give blood at 0900hrs or thereabouts so he can diagnose how you feel by having the reassuring numbers!

After reading this paper and a bunch of other points made here and there, I think that there is a a circadian driver for TSH which in turn controls FT3 production. This could come back to having Cortisol production performing in it's circadian cycle too?

T4 sits there, in the blood, in a fairly constant reserve for quick production of FT3. So what controls bound T4 & T3 - who knows. There's all those cell membrane APT dependent gates, which need FT3, to get this stuff into the cells - mind gone for the time being!!

This is really just a ramble on the control of thyroid function - for me I just cannot as yet complete the jigsaw. Who has?

As Janeb says, how you feel just wins the day.



I agree that low t4 didnt stimulate tsh for me, i had low t4 and normal tsh and felt horrendous, clear hypo symptoms. I eventually saw a private specialist and was diagnosed. I was given t4 initially but only felt a big improvement when t3 was added.

Im now on a t4 / t3 combo and guess what, my tsh is low (0.02) so they want to reduce my dose even though my t3 and t4 levels are normal, even on the lower end of normal!

Im trying for a baby, have already lost one coz they dropped my t3 and i worry so much that they just dont know enough about medicating through pregnancy.


Ta Chiquitita - more stuff that's got to be good for raising awareness.

As ever Leslie what's so totally frustrating about all this stuff is the gap between what's reasonably well known, and clinical practice on the ground.

We have on the one hand the abysmal clinical general practice we've all experienced (what doctors actually think, say and do), and the guidelines that at least some of the major endo associations publish:

On the other there's the enormous body of research which tends to again and again confirm to one degree or another what most patients and the thyroid friendly docs have actually established works in practice.

There's obviously still sizeable gaps, but the reality seems to be that the practice that most of us experience doesn't in many many cases even remotely get past the human factors - never mind into being informed by the state of the art....



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