Principles and Practical Tips for rT3, FT4 and FT3
This is from a post by Tania S. Smith on her website for Canadian thyroid patients.
I have never been a fan of putting a lot of reliance on rT3 to assess thyroid treatment. Elsewhere on the Internet and in many books there is a lot of reliance on rT3, and on FT3/rT3 ratios.
This article puts rT3 in its real context and dubunks a lot of the mythology around on the Internet.
In my latest book The Thyroid Patient's Manual, I wrote this about rT3 during treatment:
"Reverse T3 - if progress is not going well, a conversion problem might be considered as a possibility. So, if FT3 is not increasing enough, or symptoms are not improving, testing FT3 and rT3 at the same time (same blood draw, so they are consistent in time), might be a good idea. A mid-range (or lower) FT3, and high rT3, would suggest there was a conversion problem, especially if someone is not improving after dosage increases. However, I do not believe there are any specific target levels for rT3, or an ideal ratio of FT3:rT3. You have to use common sense when interpreting the FT3 and rT3 levels together, perhaps seeing how they change during treatment, together with symptoms and signs."
This is pretty consistent with what Dr. Smith has written.
Dr. Smith's article is a follow up to this one which highlights where some of the confusion surrounding rT3 may have come from:
Enjoy the articles.