Very important question

[diogenes]

A poster here replied to my post on Bianco's recent paper with a very fundamental and interesting question, pertinent to T3-only users. with no thyroid. That is, how can the model work when there's no T4 from the thyroid to make either T3 or rT3. Any replies with figures and date for FT4, FT3 and rT3 from such patients will be very illuminative. My reply to the poster is:

That is an excellent and vitally important question. If as you say there is no T4 whatsoever, then rT3 cannot be made in a T3-only situation. There are two possible answers: first I think it's rarely seen that there is no T4 whatsoever - ie a tiny bit of thyroid might be still active. Second, the system would work, but the relationship between D2 (now redundant with no thyroid and T4) and D3 (also redundant for making rT3 from T4) is much less stably maintained, because the T3 offered is controlled only by oral dose and not internal T4-T3 or T4-rT3 conversion). Also as you say there ought to be little or no rT3. I'd like TUK posters on long term strictly T3 only and no thyroid to let me see any FT4,FT3,rT3 results they have in the past with date (anonymous if possible).

I'm repeating this to reach a wider audience.

[Kitten44]

Might be good to contact Paul Robinson, as he may have access to individuals who've been on just T3. This is also an interesting question for patients to consider their therapy and opting for combination or T3 monotherapy if they have no thyroid.

[Musicmonkey]

What about conversion in other tissues in the body though?

[helvella Administrator Thyroid UK in reply to Musicmonkey]

If there is no T4, there will be no T4 > T3 conversion!

Or am I misunderstanding your point?

[Musicmonkey in reply to helvella]

I'm not sure what I mean either! Is T4 made in other tissues, or only in the thyroid itself?

[helvella Administrator Thyroid UK in reply to Musicmonkey]

So far as I am aware, only in the follicles of the thyroid.

(With some rare exceptions such as struma ovarii.)

[jan61]

Hi DiogenesI have been on T3 only now for about 8 years. I can give you bloods for T4 which is extremely low and T3 in next few days after bloods tomorrow. I don't have rt3 tested but did have it done initially as was suggested to me to see if I had any rt3 issues. I had that and thyroid antibodies done which was off the scale but interestingly my rt3 was below the labs ref range which they couldn't explain. Don't know if this helps you at all? X

[diogenes Remembering in reply to jan61]

Thank you your offer, but I need someone eg totally thyroidectomized, with FT4,FT3 and rT3 numbers when on T3 only.

[UrsaP]

Does this relate to those who have had thyroidectomy only? I haven’t had TT but I have no idea as to the physical state of my thyroid, I have extremely low T4 levels and have been on T3 mono for about 11 years.

[diogenes Remembering in reply to UrsaP]

Perhaps a look at the FT3/rT3 ratio would give some signals.

[UrsaP in reply to diogenes]

Thank you. I don’t have a rT3 reading. But will look into getting one.

[Hidden]

"There are two possible answers: first I think it's rarely seen that there is no T4 whatsoever - ie a tiny bit of thyroid might be still active. "

More significantly, there is certain to be differences between those who simply had just a total thyroidectomy and those (like myself) who voluntarily opted for RAI as well.

It seems to be standard practice that surgeons are unable to remove every bit of the gland without endangering the life of the patient.

[Lulu2red]

Fact remains, with thyroid or without, conversation issues or not. The body needs adequate T3 and in range T4. My question has never been answered. T4 is a storage hormone which converts to active T3. But it must have other mechanisms and the heart cannot work well without both hormones expressed. Hopefully someone can confirm what T4 does apart from store or convert. It is expressed in the liver kidney and brain, an3 in almost every cell in the body. T4 must have another reason to be there other than be a storage hormone.

[Jazzw in reply to Lulu2red]

Fact remains, with thyroid or without, conversation issues or not. The body needs adequate T3 and in range T4.

Does it? Why?? Adequate T3 I understand. But there are a lot of us who don’t have in-range T4.

[tcpace in reply to Jazzw]

Take my wife for example. She's T3 only and despite having only 1/2 of a thyroid, her T4 is typically way out of range, i.e. less than 1. She can't tolerate T4. It makes her feel ill, almost as if she's over-medicated. She actually takes 40-60 mcg T3 daily without feeling over-medicated in the slightest. Can anyone explain that?

[Jazzw in reply to tcpace]

Well, that’s why I was asking Lulu2red why in range T4 was needed.

If you only take T3, the body can run on that perfectly well—it doesn’t seem to need T4. Or if it does, it’s not clear what for.

It’s my understanding that 40-60mcg liothyronine is a fairly standard thyroid hormone replacement dosage for someone not on any levothyroxine. She wouldn’t feel overmedicated because, well, she probably isn’t!