Thyroid UK
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Reverse T3 and free T3 ratio

Hi, I am writing on behalf of a friend and we are trying to work out the above ratio. The numbers are: free T3=3.1 pmol/L and her reverse T3 is 0.40ng/mL. We have tried converting them to the same units, using the ratio calculator on stopthe thyroidmadness.com and many others and each time we get a different answer. I cannot find an authoritative source on how best to do this conversion. Converting to the same units of measurement, using different ones which some ratio calculators seem to allow... any help would be most appreciated.

Thank you

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There was a similar post and thread a few days ago. This article explains why this ratio is simply nonsense maths and not indicative of good or bad thyroid health. tiredthyroid.com/rt3-3.html

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I don't read tiredthyroid.com as saying that the ratio is nonsense. It simply points out that the ratio by itself doesn't tell you the whole story. Profile II is a common situation and tiredthyroid.com points out that benefits may be achieved by reducing T4 and increasing T3.

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No it's not simply pointing out that the ratio by itself doesn't tell the whole story. It's saying explicitly that "If a low ratio can be from both high or low Free T3, then the ratio is useless, because it can mean two different things; this makes it mathematically invalid." Two entirely different points. It's not arguing that looking at both FT3 and RT3 levels isn't useful, but that the ratio itself is nonsense maths.

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Totally agree with both you and tiredthyroid!

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Well, the way I look at it, the ratio is simply one piece of information to be taken in light of the rest of the situation.

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I have read that RT3 is part of the conversion when taking levothyroxine, i.e. T4, converts to RT3 and then into T3. Read the Q/A on March 24, 1999

web.archive.org/web/2010103...

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shaws Can you point specifically to where Dr Lowe is saying there is a sequential conversion of T4 -> RT3 -> T3 please, as I can't find it. Thank you.

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Shaws,

T4 converts to T3 and rT3. rT3 converts to T2 which converts to T1.

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