I created a small Excel chart the other day.
The orange lines represent the reference intervals for Free T4 tests in 17 different UK NHS Labs. (The grey is just the part between zero and bottom of reference interval.)
This is only intended to illustrate how varied they are. The orange in the top one only has a small overlap with several others, for example.
Wow, #12 goes pretty high and #15 is the smallest and likely the best place to live with a thyroid condition?
Absolutely shouldn't be!
It ***should*** be the case that if you are tested and have a result at the bottom of the range in one lab/area, you'd also be at the bottom of the range in the other sixteen! (Or top of range, of course.)
But it does make clear, I hope, that a result like 15 could be over the top of range in one lab, but a mere 25% (approx.) up from the bottom elsewhere. And that is why we always, absolutely without fail, need FT4 reference intervals.
in theory it shouldn't make any difference ... (mind you, i do have some doubts about the reality)
If you took the same blood sample and sent it to #12 and #15 the actual 'number' for the result would be different for each test even though it was the same blood sample .... but the place on the range ought to be the same . (below range / mid range / over range etc)
eg . someone with low T4 might get '7' on a test that had a [7.9-14] range ..... and '11' on a test that had a 12-22] range .
someone with mid level fT4 might get '10' on a [7.9-14] test , and '17' on a [12-22].
someone with high fT4 might get 15 on a [7.9-14] , and 24 on a [12-22]
That explains it quite well. Thank you.
Yeah, WoW!
The 'noise' coming from the results out of these labs is bound to be discordant
No wonder there is a lack of harmony in thyroid towers!!
awesome! So insightful 👏
Well that explains my confused ask for help in my post here the other day!!! That is shocking.
healthunlocked.com/thyroidu......
Yes!
On the one hand, we can use the logical and mathematical approach of percent through range. But on the other hand, we don't see consistent numbers. Whether just the number or when translated into percent through range.
just read the pervious post of yours Gilbo ... i think it works to your advantage . .... keep hold of all three (or 4) different sets of results and details .. and next time anyone suggests a dose change you don't agree with , put them under their nose and ask them to justify how a shonky blood testing system capable of giving such differing results can possibly be relied on to make life changing dose decisions ? .... and ask them to look at the full picture instead of just blood results to decide your dose.
Nice to find an endo curious enough to try and get a proper comparative test done .. shame it didn't turn up ... wouldn't be surprised if somebody wrote 'unecessary' on it and refused to pay for it .
i have some links somewhere (in an older post) to research which found significant differences between fT4 and TSH from some tests using different test platfroms . (enough to affect diagnosis /or not).. i will add them when i find them. might be a few days . supposed to be busy doing something else today.... allegedly .
Hi. I am a only a few weeks in but found this chaps explanations useful
youtube.com/watch?v=hKmOewm...
About 26 minutes in they is discussion about T4 range.
Easier to screen shot slides on this presentation from him. He presents on NICE guidance day as well - here
The interesting appearance of these test source ranges is not only are they significantly different in setting lower and upper range limits, but also the range spread can vary independently. This is as clear a demonstration of the inadequacy of test consistency as could be found. I suspect there are two factors here, 1) the manufacturers range set, and 2) the revisit by the labs concerned of determining their own range limits. The latter can be greatly distorted if either not enough subjects were used to get the range, and/or the subjects chosen were all healthy.
I noted one lab expressly stated that they use ranges as published by the Association for Clinical Biochemistry - I think using the document from 2006:
british-thyroid-association...
Which was supposed to be reviewed at least ten years ago. And should have been withdrawn once it reached its review date (or updated). (And I have tried in vain to get an actual error in it corrected. Even communicating with G Beastall an author - who agreed with me.)
Reference Ranges
TSH reference ranges
Fingerprick tests reference ranges 
New paper on TSH and FT4 reference ranges
Why do labs change reference ranges...?
