How to calculate rt3?: Hello In my country we... - Thyroid UK

Thyroid UK

131,718 members154,140 posts

How to calculate rt3?

Meavis profile image
5 Replies


In my country we use:

0.22-0.54. Nmol/l. My was 0.33 rt3

So that is: 14.33- 35.16 ng/dl. 21.48 rt3

I am not sure if I just can convert all number to ng/dl

So I have to be 2 point above but its a different range then 10_24 ng/dl. That would mean if I calculate that 12 is a good level, 2 points above it's 14%.

14% of my range is 0.26 nmol/l

14% of the other ng/dl is like 17.23 ng/dl

That would mean I am just a little high. Because it looks high 21 but you use other ranges and I am 14 in yours? I hope compared it good? I use the endo rt3 conversion model but I have difficulty with the 2 point above bottom comparing??

I am doubting because some told me that 21 ng/dl is to high that it does not matter wich range you use? That in my lab starting at 14.33 is just because more people did have rt3 high and that is why they start so high. Is this true? Can somebody help. How would no know if rt3 is low if the bottom level starts at 14.33 ??

5 Replies
greygoose profile image

It does matter what range you use. You should always use the range used by the lab that did the blood analysis. But, you don't need to convert or calculate. A range is a range, and if you are inside it, it's OK. In your original test - 0.22-0.54. Nmol/l. My was 0.33 rt3 - you are within range. It doesn't need to be translated for us to understand that. You do not have high rT3.

Besides, rT3 is a red herring. It doesn't mean much even if it's high. It means you have a problem somewhere, but the test does not tell you where. So, it's other tests that are more important. Like your FT4. If your FT4 is very high in-range, or over, then you will have high rT3, that is a given. But, it's ok.

Or, you could have high cortisol or low ferritin or low-calorie intake, or an infection causing high rT3. In which case, it is those things that you should address, and not be worrying about rT3.

But, you don't even have high rT3, so there's no problem. :)

Meavis profile image
Meavis in reply to greygoose

Hi greygoose

Thank you for your answer. But I am correct that if i do the conversion I am at 14 on a range from 10-24? It is just confusion as some say I do have very high rt3. I just want to know how to compare.

greygoose profile image
greygoose in reply to Meavis

I couldn't tell you. I'm terrible at maths!

Some people talk a lot of rot about rT3! Forget them. And forget it. Knowing your level of rT3 just won't get you anywhere. It is not the missing link that some people believe. :)

MaisieGray profile image
MaisieGray in reply to Meavis

Meavis If your rT3 result was 0.33 (0.22-0.54 Nmol/l) then it is not high because it is within the reference range; and it is not even 'high in range' either because it is just below midway within the range. That is all you need to be concerned with, there is no merit in converting it to anything else. And I echo greygoose, in that much of what is said about RT3 is best ignored.

Angel_of_the_North profile image
Angel_of_the_North in reply to Meavis

The point is that it doesn't matter as that is not the range used by the lab doing the test, and that's the only one that is accurate for your results. YOU DO NOT HAVE HIGH rT3! It is less than 50% (about 31%) through the range and that would be about 14.34 in the other, completely irrelevant range

You may also like...