On this forum there are several different ways of recording reference ranges for FT3 and FT4 which can cause the utmost confusion.
Just for the record, I compare the world's (Incl UK) ranges and the US ones as both come on to this forum with their own ranges:
Normal range for FT3 in pmol/L (UK and everywhere else sensible) 3.5-7.
In the USA 2.0-4.4 pg/ml
Normal range for FT4 in pmol/L (UK and everywhere else sensible) 10-25 pmol/L
In the USA 0.9-1.8 ng/dl
My labs in the Thames Valley are different.
T3 is 3.9 - 6.7 and T4 is 12 - 22.
They have been like this for years. Are you familiar with these ranges?
Yes, it's not the exact ranges for the different ways (pmol/L. ng/dl etc) of expressing that I'm dealing with, but the actual basic difference in the units used and the confusion it causes to people trying to respond to posters. Eg in calculating FT4/FT3 ratios.
I think I read something recently that you've written saying that the American units of measurement make it impossible to work out a Free T4/Free T3 ratio because they aren't in the same units, and are actually measuring something in a completely different way from the way that UK measurements are. Something to do with the molecular weights?
Can the American units of measurement be converted to pmol/L ?
Easier just to work out how far through the range each one is and if the FT3 % age is way lower than the FT4 % age you have a conversion problem. If the FT3 is higher in range than FT4 and TSH is over 3, you have the beginnings of hypo. Not really sure if anything else really matters
Very good point!
Not sure if I am missing something but searching for a converter on the internet I get the following, which would suggest you have the American T3 and T4 transposed.
3.5 pmol/L = 0.95 pg/mL
7 pmol/L = 1.91 pg/mL
10 pmol/L = 2.72 pg/mL
25 pmol/L = 6.81 pg/mL
Does it matter if FT4 is over range to increase FT3
FT4 high in range, FT3 over range - still feel bad. Am I pooling?
What is the NHS FT4 reference range?
TSH, FT3 & FT4 results
FT3 at bottom of range
