Thyroid UK
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The Lab have lowered their Free T4 reference range

It has been a year since my last bloods. My Free T4 was 23.9 and the reference range was 12 to 22 and now it is 9 - 19.

I am usually above the reference range and my TSH is <0.01 and my Free T3 5.4 (2.6-5.7)

My GP is on holiday so I spoke to another one asking why the reference range had been lowered. She said that she would write to the lab asking them but doesn't know whether we will have a reply :-(

I said so if you see someone who usually has a Free T4 of 20 who as ok with the last test under the previous range, but now you will be suggesting that she reduces the meds??? crazy crazy and then just 13 miles away the lab range for Free T4 is 9 to 26 !!!!!!

I am fortunate that I am not nagged by my GP (a. because I keep well away from the surgery and b. because my Endo says he is happy with my levels.

I am thinking of all of the hundreds of people out there who are already struggling to be fully medicated because their GP goes by the TSH, this is just not going to help at all!!!!!

I feel better now!!`!`


16 Replies


Changing the reference range does not mean that someone will have to adjust their dose - or at least, that is not necessarily the case.

If we imagine that they have introduced a new testing machine. Then the following could be the case:

Any sample that gave a reading of 12 on the old machine would give a reading of 9 on the new machine.

Any sample that gave a reading of 22 on the old machine would give a reading of 19 on the new machine.

If so, the only difference would be that the numbers are all 3 lower on the new machine than the old. And if they still have the old machine that could be checked out.

The FT4 ranges are established (typically) to ensure that if they take the blood of people without a thyroid disorder, then approximately 2.5% are below the bottom of the range, and another 2.5% are above the top of the range.

If you moved all the people being tested from one lab to another, they should still be in or out of range, in exactly the same pattern.

However, it is also possible that subtle differences or even policy changes also apply. So it is as well to ask the lab. Expecting a GP to do so is probably not the best way of ensuring a comprehensive answer. Could try the lab directly, the local PALS service, and even mention the Freedom of Information Act (under which such things should usually be accessible to us).



This makes things awkward for people at both end of the 'range' it seems.

Here where the range is from 9 - 24 you need to drop off the bottom before help. In Berkshire the range is 12 - 24 so if you have a reading of say 11 you are treated or not depending on where you are.

Unless Rod you are saying that the methodology is also somehow different or the machines are calibrated differently which accounts for changes in the 'range'? In that case I can see your thinking.

If the same sample was tested in both areas (on differnt range machines) then one would come out at 11 in the 9 - 24 range and the other would come out at say, 14 in the 12 - 24 range yes?


Your last sentence is spot on.

If the issue is that the machine (or some other aspect of the technology behind testing) has changed, then you are seeing it exactly as it is.

Without contacting the lab, we cannot be sure exactly what has happened. It is also possible that the lab has re-done their calibration against the population.

The bottom line, though, is that we have to treat the reference ranges as being specific to a laboratory and a time. We simply do not have the information, nor understanding, to do otherwise.

There are some ranges now that almost do not overlap at all. E.g. 7-14 and 12-22. Quite obviously someone with low FT4 would expect to be near the bottom of the ranges whichever test they had. They certainly would not expect to have a result of, say, 13 at both!


Thanks for your reply Rod. I don't understand.

On any machine old or new or different areas wouldn't my result be 23.9?

So in Coventry I would be under the range of 26 but now with my new maximum of 19 I am almost 5 above?


No - you would have different numbers on the old and new machines.

In some ways it is a bit like Fahrenheit and Celsius (Centigrade) temperature scales.

Two scales, freezing point and boiling point have different numbers, but mean the same things! That is, 32 F is same as 0 C, and 212 F is same as 100C.

(Not such a big difference, but the same idea.)


The labs my gp uses have changed but my ft4 remained the same but, they only changed the bottom number.

The old range for ft4 was 9-17 and the new range is 7-17.

Its mad as a few months ago my ft4 was around 20 which was classed as having way too much thyroxine but, in a different lab (private) with the result i had of 20 (the same) it looked like i had room for improvement as the top of their range was 24??!!


Hi Sometimes this happens because of the "Powers that be" but sometimes it is just that a Lab has altered its method of analysing, like different Labs have such different ranges, it is usually the methods of assay they use. It should not make any difference in that case.



That's happened to me, I was around about 25 - 26 which was slightly above but fine. A new doctor said that was too high now because the labs had changed the reference range reduced my thyroxine because he,said I might have stroke even though no hyper symptoms. I was feeling so Ill that I went back to see another doctor because my T4 had gone down to 12.


Lesley, I do hope that you have increased your meds and are feeling ok.

I am still yet to see any evidence that having TSH suppressed and free t4 just above range causes heart problems.

I feel well and certainly not over medicated. Why would we lower meds so that doctors like our numbers but feel so unwell. When I have tried to lower meds I need a nap in the afternoon and cannot do any exercise. I have my life back now and I don't want to lose it again.

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I have just had blood results back this month. I was informed that TSH range was .35-3.3 now .35 - 4.5. I wonder who decides our Fate.??

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My GP called me 'weird' because I was having trouble taking my thyroxine - charming! I was diagnosed hypothyroid 7 years ago but have had problems taking thyroxine because every time i take it (just a very small dose) I just feel hyper with sweating and fast pulse. So glad I found this site because it seems I'm not so weird after all!!!!

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Starlight, glad you found us! Have you been given a different brand of levothyroxine? Have you ever managed to tolerate levo in the 7 years?


Sorry, I'm confused - let me get this straight:

Depending on what lab my bloods go to depends on what range is 'normal' and what my doctors treat me off?

I'm currently in a battle because my T4 is too high and my TSH is pretty much (not quite) suppressed and I actually feel good.

I keep bringing this up - treat me off my symptoms not stupid numbers. What is normal anyway? I'm also in the thyroxine war.... pharmacist says brand hopping isn't good, doc says it's rubbish. Oh my.

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Oh dear Hayface, I am waiting for a reply from the labs via my GP as I just don't get it.

The way I look at it is this, there are very few of us who know what our thyroid blood levels were like when we were well prior to our thyroids packing up on us.

My guess is, is that my tsh was suppressed and my free t4 was above the so called lab range before because this is how I feel well on the dose that I am taking. I just don't care what my numbers are.

The levothyroxine makes - having a good relationship with your Pharmacist helps. Which one suite you?


This is exactly what has happened to me and it has completely thrown me. I used to know where I was with the results but now I really don't. I was always in the range of 20-25 but now I am getting 9-10 and I haven't a clue what the exact reference range is now. Why can't they just leave well alone?


If a lab needs a new analysis machine, then it is very likely to come with new ranges.

There has been a tendency for lab ranges for FT4 to go down (top and bottom of range). That might well indicate an improvement in consistency. On that basis, I would be perfectly happy for ranges to change and upset if they don't keep things up to date. :-)

However, it would be most excellent if tests could be consistent and accurate - and ranges were the same everywhere.



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