When Darcey and I talk about thyroid hormone levels we usually refer to the percentile of the reference range. For example: I might say, my FT3 is 47% and my FT4 is at 30%. It’s easier to compare and record on our spreadsheets when it is converted to percentage of range. It also keeps things simple when you have different labs assays and reference ranges. For instance, I live in the USA and Darcey lives in Canada, the pmol/L to ng/dL conversion gets confusing and tedious.
It’s quite simple to figure out your percentage rage. I’m an English major and even I can do it!
Here’s the simple formula ~
Result – Bottom of range ÷ Top of range – Bottom of range = % of range
So let’s take my current labs and figure out their % of range using the above formula.
FT3 2.8 (reference range 2.3-4.2)
FT4 1.49 (reference range .8-1.8)
The math looks like this ~
2.8 (my FT3 result) – 2.3 (bottom of FT3 reference range) = 0.5
4.2 (top of FT3 reference range) – 2.3 (bottom of FT3 reference range) = 1.9
Divide the results 0.5 ÷ 1.9 = 0.2631
My FT3 results are 26% of the range.
Let’s do it again for my FT4
1.49 (my FT4 result) – .8 (bottom of FT4 range)= .69
1.8 (top of FT4 reference range) – .8 (bottom of FT4 range) = 1
Divide the results .69 ÷ 1 = .69
My FT4 results are 69% of the range.
So there you go, it just seems easier to talk about and compare lab results when they are presented equally in this fashion.