Thyroid UK
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Can someone explain the reason for different lab ranges?

To an extent I can understand why you would have different ranges in different countries but why do the ranges differ from lab to lab here in the UK? They're not using different units are they? For example for tpo ab....I have seen 0-34 as a very common one but the place where my bloods were tested the range was 0-100. So my first result of 92 was negative with my lab but had it been done at a 0-34 one it would have been strongly positive. Am I just being thick???

5 Replies

When it comes to antibodies, some labs scale the results.

So if the actual range in the lab is 0-34, they would multiply by about 3 to make that 0-100. If the actual range were 0 to 1000, they would divide by 10. Or whatever. This is because the actual numbers are so extremely variable depending on the technology of the test - if they scale everything to a 0 to 100 range, it makes it easier when reading the results.

But some labs use the numbers as they are!

Don't think this is in any way different in the UK. Every country I have read about has different ranges from one lab to another. (Maybe somewhere with very central control is different. But I have not noticed it.)

Within the UK most labs use the exact same units for most tests. And there are committees and organisations to try to make that so. But we need to be careful because occasionally that is not so.



Ahhh now that makes complete sense. I mean it's still rather stupid that they use different types of technology but now I understand how it works.I'm glad I asked because it was really confusing me.

So you say that for this is for antibodies...does it work the same for things like tsh and ft4? As I have noticed they can vary too. Does the same thing apply?

Thanks for taking the time to explain Rod...much appreciated :)


Not many tests are scaled to have a 0-100 range (or similar) - most use the values that come out of the tests. But in logical terms, yes, tests do vary and you absolutely must use the appropriate reference ranges.

For some tests there are well-defined techniques for ensuring that labs get near-identical results from the tests they do. Then use effectively identical (or almost identical) ranges.

For reasons that vary tests such as TSH, FT3 and FT4 all vary - by quite some margin. The test manufacturers should hang their heads in shame that they cannot achieve very much closer results than they do. I guess some justification does exist in that as years go by, there are improvements in the tests so the newer (and, hopefully, better) tests might have different ranges because they are better. Then it can take many years for the other companies to catch up and possibly overtake the competition.



Hi That is why the ranges are always vital for all blood tests. they use different assays, fine if have the ranges.

Best wishes,



Yep totally get it now. I thought the ranges were just needed to see if you were in middle,bottom or top but now I understand there is more to it. Thanks Jackie.


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