When is 5.6 not 5.6

For as long as I can remember my FT3 has been 5.6 with a consistent dose of 2 grains of Thyroid S and a consistent range of (3.4 - 6.8).

18 months ago I moved to another part of the country where the FT3 range is (2.5 - 5.5). Technically my FT3 is now over range although no one seems to be too worried about it.

That said , it’s ‘bugging’ me. It makes no sense. I’ve heard that ranges are derived from the average of the tested population just as the ‘pass mark’ of examinations in higher education are calculated from the average mark achieved by the cohort being tested. That’s slightly more understandable as there’s a finite number of college / university places.

But blood tests? Why oh why?

[DippyDame]

I think you might be mixing apples with pears!!

It might be easier/clearer to calculate the lab result as a percentage through the ref range and compare that number after each test

It doesn't matter then that your new labs/ ref ranges differ from the old ones.....the percentage through the ref range will be the same

Old labs...

FT3 5.1 (3.1 -6.8.) = 64.71% through ref range

The lab result in your new area is different to your old result because the test machine is calibrated differently.

But... if you use your new result with the new reference range your percentage is likely to be the same/ similar to previously

Handy calculator -

thyroid.dopiaza.org/?utm_so...

Fill your new lab test numbers into the calculator and check

Given that, are you now sure your result is over range in the new ref range?

Hope this helps.

[Hidden in reply to DippyDame]

It certainly does and thank you.

I have a tendency to overthink things but on this occasion it seems that I was looking for a simple explanation which does not exist 🙄

Yes. Using the calculator, my labs are the same.

Thank you

[DippyDame in reply to Hidden]

You're welcome!

Take care.