Hi all, endo recently poo pooed any idea of non conversion of T4 to T3. Also, he didnt' mention testing for Reverse T3. Any known links to authoritative, medical documentation for these, please?
RT3 and not converting T4 to T3 - links to auth... - Thyroid UK
RT3 and not converting T4 to T3 - links to authoritative sources of these occurences?
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cc120
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CC, according to my endo rT3 isn't tested on the NHS. I've seen one post where member who has had rT3 tested on the NHS so I think it is as rare as hen's teeth. If your TSH is low, FT4 halfway to 3/4 through range and FT3 low there is a conversion problem although you will be converting some T4 to T3.
Thank you Clutter, so NHS and endos don't recognise RT3, and think that non conversion of T4 to T3 is very rare?
CC, some NHS endos and GPs do recognise poor conversion is an issue but many don't. They won't see there is a problem unless they measure TSH, FT4 & FT3 and even then many think low FT3 isn't important. My endo wasn't bothered when my FT3 dropped below range so I started self medicating. 6 months later he acknowledged the improvement in my health and prescribed T4+T3.
Hi Clutter, amazing that they don't recognise this still. Only reason my FT3 was checked was that after over 7 years of high TSH and symptoms being ignored by GP, after self-medicating with NDT my TSH became suppressed. So was finally got referred to endo when i asked for FT3. Just before appt with endo, GP sent a letter stating the lab agreed to test FT3 (but had this done at the hospital was due to see endo). I have read that NHS labs are supposed to test FT3 if TSH is suppressed, so they should have tested when they found TSH suppressed.
CC, I think it is more common to find that labs won't test FT3 unless TSH is suppressed unless a GP or endo specifically requests FT3 and even then GPs may have to chase the lab up on FT3 while they still hold the sample if it isn't done.
This might be helpful but as Clutter said RT3 is generally not recognized as a problem in the UK nor the US by standard allopathic docs. Look through the topic list and check the graphs. PR
nahypothyroidism.org/deiodi...
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).
Thank you, I wonder if that is a source that GP or endo would respect?
National Academy of Hypothyroidism - Helping Doctors ...
The National Academy of Hypothyroidism is a group of thyroidologists, headed by Kent Holtorf, M.D., who are dedicated to the promotion of scientifically sound ...
They support what they say with scientific studies. I would think they would.
That sounds reasonable, thank you.
cc, are you saying they don't believe reverse T3 is contributing to non conversion? Or, do they feel reverse T3 does not exist. If you use Galathea's link (PubMed) and put reverse T3 in the search, it will come up with lots of articles that mention reverse T3. Often it is "low" because of physical defects of some of the subjects used. Everyone has some reverse T3. It's one of the ways to control the amount of free T3, I think, so you're T3 levels don't go too high.
May I refer you to Clutter's post above which I have pasted here so you don't need to search for it:
Clutter Administrator
CC, some NHS endos and GPs do recognise poor conversion is an issue but many don't. They won't see there is a problem unless they measure TSH, FT4 & FT3 and even then many think low FT3 isn't important. My endo wasn't bothered when my FT3 dropped below range so I started self medicating. 6 months later he acknowledged the improvement in my health and prescribed T4+T3.
According to Dr. Lowe, achieving optimal therapeutic results for many patients depends on them rejecting T4 replacement.
cc, do you expect whomever you are trying to prove this to, will except anything you bring to them? Usually they reject anything they do not agree with as Clutter seems to point out.
It's about time they start accepting the proven research and papers written scientifically. But i wouldn't hold my breath. Here's a list you can peruse.
OK, here's a dumb question which I'm asking here because some of you may know the answer - ( I'm mindful of Louise's warning about straying off-topic, but keen to take advantage of the knowledge of those contributing above ) - Can rT3 be produced from T3 alone? I understand that rT3 is produced by deiodination of one of the inner rings of the T4 molecule rather than from the outer ring, which produces T3, but when you're on T3 only and TT, is the T3 you take already 'fixed' as active T3, or can it be converted to rT3?
I'm aware that rT3 is useful in regulating the total amount of fT3 reaching the cells, and curious as to whether that mechanism is available to us T3 only types?
Mickstability, I'm also interested interested in this question! I'm taking mixture of T3 and T4. I have recently seen Dr Chapman, who suggested and tested me for three ways my body might not be using that thyroxine. Converting the T3 into rT3 was one of the ways. So that suggests he thinks it can can happen. But I don't don't have any more detail than than that.
No, rT3 can only be produced from T4. HOWEVER, if someone takes too much T3 (who has T4 available in their body), then they can create more rT3 from the T4, as a protective mechanism so they don't become hyper. This happens often on someone taking desiccated thyroid. The more they take, the higher their rT3 becomes. NDT should, be definition, also contain rT3, since it's produced in a normal thyroid gland, like T3. A lot of reading here: tiredthyroid.com/rt3.html
Thanks HIFL - that's what I wanted to know: I was concerned that if I take more T3 than I need there would be no 'natural' compensating mechanism to convert it to rT3, other than to wait until it was metabolised out. So now I know... On the rare occasions it's happened whilst taking a steady dose of 80mcg per day, I've found that the symptoms pass, and I can carry on as normal. Thanks for the link.
By the way, I don't think NDT contains rT3 per se, only the potential to convert it from T4. As I understand it, the deiodination of T4 to rT3 would take place AFTER it had left the thyroid gland. I may be wrong. Helvella or Diogenes could clarify this 
Mickstability, that's my understanding too. T4 converts to rT3 and T3 (can't remember the ratios) to regulate FT3 and prevent it going too high.
Or Clutter! (See above)
NDT is made from thyroid glands. The glands make T4, T3, rT3 and a trace of T2. Here's where I read it: tiredthyroid.com/blog/2012/...
But you're correct that everything except T4 can be made from deiodination elsewhere in the body, including rT3.
Thanks, I think(!) - I'm still absorbing the info from the tired thyroid site you linked. A lot of VERY interesting stuff there, much of it confirming my wish to move from synthesised T3 to NDT - particularly (but not exclusively) the stuff about T4 not being an 'inert' pro-hormone, ( I always thought that if T4 itself had to be broken down into 3, 2,1,0, to be useful, then the '4' component should have a function; see her stuff on INF-y [ gamma interferon ] for instance ).
There is a huge amount of assertive opinion on the Tired Thyroid site, and I'm going to have to spend a good deal of time figuring out what's supported by sound clinical research, I reckon!
helvellaAdministratorThyroid UK
There is quite a lot about rT3 in this Thyroid Manager chapter:
I will try that reallyfedup123 : )
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