Q&A Doctor Series: Thyroid Resistance, Introducing T4 Medication, and Free T3/Reverse T3 Ratios (Answer by David Borenstein, MD)

[PR4NOW]

An interesting post on ThyroidChange.org that may be of interest to some on here. PR

thyroidchange.org/our-blog

Following that is a post on Thyroid care in Arabia which is also interesting.

[gabkad]

Interesting yes, but if you look up vitamin D levels in women and men in Saudi Arabia it's 4 ng/ml. Even if they aren't wearing full body covering, they stay indoors all the time. I suppose the only reason their children don't have rickets is because they are fed formula.

[shaws Administrator]

Thanks very much. Very interesting articles.

[humanbean]

The discussion of T3 ratios always baffles me because my numbers never make sense. I noticed that this article actually specified that the units must be the same for both Free T3 and reverse T3.

So, in the spirit of the article, can people tell me where I'm going wrong :

In 2013 I got the following results from Genova testing - note the different units.

Free T3 = 6 pmol/L (Range : 2.8 - 6.5)

Reverse T3 = 0.72 pmol/mL (Range : 0.14 - 0.54)

If I convert the Reverse T3 into pmol/L I have to multiply my result by 1000, so I end up with a Reverse T3 figure of 720 pmol/L.

The article states :

"Some physicians compare the ratio of T3 to Reverse T3 - and consider certain cutoff points to be evidence of dysfunction. For example, some physicians feel that the Free T3/Reverse T3 ratio should be at least 20. (That means, that if Reverse T3 is 10, Free T3 should be at least 200.) "

"Keep in mind that you need to use the same unit of measurement for the Free T3 (or Total T3), and the Reverse T3. "

If I calculate the ratio for my numbers I get 6 divided by 720 = 0.0083. <--- Should be at least 20 for good health, apparently, so I've got my work cut out!

My BS detector is quivering like mad.

[helvella Administrator in reply to humanbean]

But are you looking at the right rT3 and T3 measurements? I freely confess to confusion because of the numerous different opinions and formal analysis of the issues. But surely it should be free rT3 against free T3? I had understood rT3 tests are usually Total rather than free.

[humanbean in reply to helvella]

The idea of Total rT3 and Free rT3 appears to make sense, although proof of the existence of Free rT3 would be welcome. I have to admit the concept had never crossed my mind before now. I've never had Total T3 measured, so it looks as though I'm never going to be able to calculate this ratio. Doh!

[helvella Administrator in reply to humanbean]

I have an inkling that it came up in a discussion with diogenes at some point, quite a while ago.

I have no idea of the typical proportion of bound to unbound rT3.

[humanbean in reply to helvella]

Thank you, Rod. I imagine many GPs have never heard of reverse T3 (mine certainly hadn't). The idea that it can be bound or unbound would make some doctors' heads spin, I think.

[PR4NOW in reply to humanbean]

HB, here is another opinion.

tiredthyroid.com/blog/2011/...

And this is from the RT3 Yahoo group site which had moved.

thyroidrt3.com/

This is their page showing how to look at labs.

thyroidrt3.com/examples.htm

I'm afraid this is an area that is still full of differing opinions. PR

[humanbean in reply to PR4NOW]

Thanks for the links, PR4NOW. I've seen similar examples before, in connection with the ratio between T3 and reverse T3. But most of them seem to be about "making it up as you go along". The idea of multiplying or dividing by 10 or 100 or 1000 just to make the numbers seem to be in the right ballpark for the ratio to be as close as possible to 20 seems to be a bodge of the first order to me. If there was any logic behind it, one would hope that the multiplying and dividing would be explained but it never is.

I understand what people are trying to achieve with this idea of the ratio, but somehow, to my mind, nobody has actually succeeded in making sensible, explainable, understandable rules.

[PR4NOW in reply to humanbean]

HB, Dr. Holtorf's take on RT3. Dr. Wright also thought it a useful marker. PR

nahypothyroidism.org/thyroi...

Reverse T3

TSH and serum T4 levels fail to correlate with intracellular thyroid levels. Additionally, the free T3 will also tend to be less accurate with reduced cellular energy. This artificial elevation of T3 due to be reduced uptake into the cell is generally offset by a reduced T4 to T3 conversion due to reduced uptake and T4 and subsequent conversion to T3, making T3 a more accurate marker than the TSH or T4 with physiologic stress. Also, the transporter for reverse T3 (rT3) is similar to T4 in that it is energy dependent and has the same kinetics as the T4 transporter (6,41,45,62,66,67). This property (among others) makes it the most useful indicator of diminished transport of T4 into the cell (45).

Thus, a high reverse T3 demonstrates that there is either an inhibition of reverse T3 uptake into the cell and/or there is increased T4 to reverse T3 formation. These always occur together in a wide range of physiologic conditions and both cause reduced intracellular T4 and T3 levels and cellular hypothyroidism. Thus, reverse T3 is an excellent marker for reduced cellular T4 and T3 levels not detected by TSH or serum T4 and T3 levels. Because increased rT3 is a marker for reduced uptake of T4 and reduced T4 to T3 conversion, any increase (high or high normal) in rT3 is not only an indicator of tissue hypothyroidism but also that T4 only replacement would not be considered optimal in such cases and would be expected to have inadequate or sub-optimal results. A high reverse T3 can be associated with hyperthyroidism as the body tries to reduce cellular thyroid levels, but this can be differentiated by symptoms and by utilizing the free T3/reverse T3 ratio, which is proving to be the best physiologic marker of intracellular thyroid levels (see Diagnosis of low thyroid due to stress & illness Graph).

Link to graph in last sentence.

nahypothyroidism.org/thyroi...

[humanbean in reply to PR4NOW]

Thanks PR. I have no doubt that the ratio between T3 and rT3 is very useful, and I realise that levels of rT3 are vitally important in determining what may or may not be happening in the body. But I'm coming at the problem from the idea that nobody has come up with a set of reproducible rules for calculating this ratio that always work. And until they do, the ratio is not a useful measure because nobody can assume that people are comparing like with like.

If I calculate the ratio between my T3 and my rT3 and I get the answer 0.0083 and I read that it must be around 20, it doesn't fill me with confidence in the number I've calculated.

I'm assuming the description of how to calculate the ratio (the instructions I read above) is actually wrong and I should have got a result of 8.33. But it shouldn't be necessary to bodge it and make assumptions like that.

I get the feeling I'm becoming more and more pedantic and dogmatic on this matter, so I will stop now because it really isn't helping anyone, including me.