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Thyroid UK
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FT3/rT3 ratio = 0.2 Not sure what this means

Further to my post yesterday, I now have the ratio. According to STTM it should be over 20!

Given that maths isn't my strong point, perhaps my calculations should be checked: 

FT3: 4.17 pmol/L

rT3: 18 ug/ L

So, the actual rT3 result is above 14 and this, according to STTM, is excessive.

The  ratio is 0.2 and should be over 20.

The result fits with a low normal FT4 reading of 15.59 (12-22).

These results are one of many I posted yesterday - please see healthunlocked.com/thyroidu...

for further info.

I would really appreciate help with this as it does look as though I finally have some clues as to what may be going on - and that there may be an underlying cause to all my symptoms.

With thanks,


6 Replies

Many thanks - I actually used the STTM calculator (see stopthethyroidmadness.com/r... and made sure I entered the correct units of measurement for each (they are different measurement units). Please feel free to double check I've entered them correctly - brain not in gear today!



I'd contact STTM for help.  There may be problems with the calculator or the conversion calculator they supply.

1 like

Thank you Clutter. In fact we had the same idea so I'm waiting a reply from them. I'll let you know what they say.


There is a problem with the STTM calculator. It's surprising how many people using UK units get an answer of 0.2!

Use these instructions to calculate it instead :



I get the following result :

(4.17 x 100)/18 = 23 (to the nearest whole number)

What are the reference ranges on your results?

For STTM to pick a particular number (14) and saying anything over that is excessive, is nonsensical without specifying the units to be used and the reference range they are comparing to.

Edit : STTM do this a lot - mention a number without units or reference ranges. It is annoying and potentially dangerous.


Many thanks Humanbean, that makes a huge difference! The ref range is 10-24 so 18 is within range.

I had hoped that the ratio results would answer a few questions, but no - back to the drawing board for me then.

I don't know if you saw the full Blue Horizon results (see the link above). Marz wonders if central hypothyroidism may be the problem, though I have my doubts. I'd be interested in your feedback.

With appreciation,

Amandak (aka ann_g_k)


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