Hello! I hope someone can help with this. It's something I've asked about before but I didn't really understand the answer and it's bugged me ever since! I don't know if it's brain fog or what, but can someone please help me understand lab ranges :)Ok so my issue is that some organisations and people in the know state that a level of something tested should be a certain test result for optimal. E.g. a ferritin level of 90-100 or a particular TSH level. But they don't give a reference range. So this leads me to think that that test result optimal level is standard no matter what the lab reference range is.
However, repeatedly I see reference ranges being used as though they influence the test result somehow? As though the test result depends on the reference range. As though the test result would be Different if tested with a different reference range? How can that be?
Surely if say your TSH test result is 5.5 with a reference range of say 0.8 to 10, your test result for TSH will also be 5.5 with a reference range of 2 to 5? How does the reference range change the actual test result? Or am I totally missing the point.
Thank you so much for any enlightenment I feel a wally for asking this!
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tinkerbell22
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The ranges depend on the equipment used in the lab. If your ft4 is say 16 on a range 10 - 22 then you get tested in a different lab you would expect your result to be at the same point through that labs range. But that same point through the different range will not be the same number. If the new range for ft4 was 7 -15 you would expect your result to be 11. Both results are 50% half way through the different ranges .
The ranges for TSH does not vary that much and is never above 5 at the top end which is why it is easy to say 1 or under.
The ranges for vitamins can vary depending on the measurement used but usually they are much of a muchness
Ft4 and ft3 are the important results where the ranges do vary between labs and these ranges are very important so we can gauge where in range the results lie
Both results are 50% half way through the different ranges .
I hope it’s OK to chirp in, as this is what I thought too. Except, using different labs for my recent ferritin result for example even though both blood tests were in the same hour of the same day, I got very different percentages.
greygoose I see you’ve stated similar below. So, I’ve tagged in case you are willing able to comment of course.
Can't comment on iron, but TSH is a case apart. Whatever the range - and ranges are arbitary at best - a euthyroid TSH is around one. And, when on thyroid hormone replacement, the idea is to bring the TSH down to 1 or under.
For an awful lot of blood tests, nutrients and things, the ranges are more or less the same, just slight variations. Where it gets complicated is the FT4 and FT3. They can vary a lot! So, what we do is work out the percentage through the range so that we can compare results with different ranges.
Ranges are calculated by taking blood from a percentage of the local population, and removing the top 2% and the bottom 2%. And the machine that does the analysis is calibrated accordingly. Which is why we get such variation in the ranges. If your FT4 is 50% through a range of 12 - 22, then it should be 50% through any other range, too. However, the actual result will depend on the range. 50% of 12 - 22 is 17. But 50% of 0.8 - 1.8 - which I saw earlier today - is 1.3.
Sorry if that's not very clear, just hope it hasn't confused you even further! lol But, maybe you'd find this article of interest:
The normal range: it is not normal and it is not a range
Sorry different query now. If euthyroid TSH is around 1, why am I always told I’m normal when all my results are between 3 and 4.5? All of this is so confusing!
Because doctors consider anywhere in range to be normal. But there is a difference between normal and optimal. Doctors don't seem to understand that you can still be unwell even if your results are in the normal range because your body works better at a different normal number in the range Imagine the range as a rail of clothes all normal sizes. According to the doctor all the clothes on that rail should fit you because they are of normal size. That's not much use to you if you get a blouse from the normal rail and find it's a 34 bust when you are a 38 bust. But the doctor would tell you it was fine and just to get on with it because the blouse was normal. And you would have to go around with buttons popping off in every direction about to have a wardrobe malfunction!
Have read your post and totally understand your point of view. Lalatoot's comments are in line with what I'd been told earlier in reply to my original post. The way I see it is that if you have (say) 551 laboratories throughout Britain you are likely to get 551 different results - all depending on the equipment the lab is using. To me, that's bordering on an Ealing Comedy Farce !!
I had a range of blood tests - full blood count - covering shedloads of issues. However everything that was tested gave a normal result except TSH which showed 0.303 compared to the range figure of 0.35. That said there were 5 or 6 tests not undertaken for a variety of reasons. So now I have to have more tests on 18 August.
My GP and I have agreed that that result could well be a testing glitch and neither of us are that fussed about it. The point is most results were normal, others were not tested at all and only 1 out of the whole lot showed a potential issue. We'll see what 18 August provides. Just hope the next lot of tests are done with the same lab - or else it really will be a joke. What a bloody mess !
This is happening to me with GP bloods too. Some were missed due to ordering issue and another due to insufficient sample. My next attempt will be my 3rd in the last fe weeks. You can not make it up!
I am so glad you posted this as I don’t get it either. I would have thought using reference ranges and calculating where in percentage in that range would be same across any test. This has not proven the case for me.
It's a 'free for all' it seems. I wonder how many GP's have written out an incorrect prescription when acting on confusing/contradictory or some weirdo test results.
Many of the ranges were set using a study group of fit young men. Now I am visualising fit young men trying on different blouses. I may have to go and lie down for a bit...
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I feel a wally for asking this!
Laboratory reference ranges
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