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Thyroid UK
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FT3/rT3 ratio - T3

FT3/rT3 ratio - T3

Hello, I am writing to ask you advice about Hashimoto's and T3.

I am currently on Armour thyroid, should I be using only t3, has anyone moved from NDT to T3? Also I'm wondering if T3 is still available in London and if someone could recommend a doctor, my current doctor doesn't think its a good idea.

From my last panel I had the attached information. I'm currently very sluggish and depressed. I gave up smoking last month and systems seem to have increased.

Your rT3 is elevated and your FT3/rT3 ratio is low which could suggest that you are not getting sufficient free triiodothyronine (FT3) into your cells. There is currently little scientific research into the FT3/rT3 ratio, but some experts believe that this could lead to symptoms of hypothyroidism (slow metabolism) even though your thyroid hormones are at normal levels.

Thank you so much,

3 Replies

No reason to be on T3 only, your high rT3 has nothing to do with your thyroid levels. Your FT4 would have to be right up the top of the range to be the cause of high rT3. Yours is under mid-range. It's not taking T3 that lowers rT3, it's finding the problem and fixing it.

All that about the rT3 ratio is medical BS. The ratio is low because your FT3 is low and the rT3 is high, and it's the low FT3 that causes symptoms - it's not getting into the cells because there's not enough of it.

So, why do you have high rT3? Did you not have your ferritin tested? Low iron could cause it, as could low calorie diets, low/high cortisol, infections, and many other things.

Your B12 is much too low, and your vit D slightly low. Can't remember if they could cause high rT3. But, you do need to do something about them. Nutrients need to be optimal for your body to be able to use thyroid hormone.

But, all in all, I would say your main problem is that you just need an increase in dose.


Thank you for taking the time to reply grey goose!


You're welcome. :)


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