I think it's all useful to everyone because thyroid stuff is complicated and the more you read about different people's circumstances, the more you come to understand it really. Not that I understand what is going on with me...
I can't do the quote-y thing Wrensong... Will do this instead:
"I imagine your low T4 results were due to your supplementing with T3, as with more active thyroid hormone in the body there would be less call for your thyroid gland to produce T4. "
One way or another, the low T4 results were due to the T3 - but whether the T3 supplementation has 'caused' them or uncovered the real issue, is the question. Because I wasn't given enough T3 to be sufficient by itself. The doctor didn't want to put me on a full dose of T3 - because the idea was to boost what my body was doing and to clear the high rT3 - rather than to replace what my body was doing. The worry about giving me a full dose of it is that I could just end up on thyroid meds ongoing, when (if it were a conversion problem) I didn't really need that. There are other sources online where people with high rT3 and conversion problems are given T3 to clear the rT3 - but they are given regular doses of it, not the micro dose I was given. (See the last few sentences here:
https://neuroendocrinology.org/what-is-the-reverse-t3-syndrome/ ) And why my T4 then plummeted despite my body needing more T3, I've no idea.
"Can I ask what your TSH was at the time of the TFT that showed the low T4? "
Normal, always normal TSH. That time it was 1.15. (The highest it's been was 3.4, that was before any medication.)
"Did the endocrinologist comment on the reduction in your rT3? "
Yes, we are happy about that - the T3 brought down the rT3 as planned, from 33 to 15. It should really be lower than that, but 15 is borderline okay. I am re-testing rT3 in January, even though it takes ages to get the results back for that and has to be a venous draw. Because now I'm taking T4/levo, I want to check I'm not just going to convert that to rT3 again(!).
"but if you don't have raised thyroid antibodies (sorry, can't remember for sure) that shouldn't apply to you. "
I don't have raised antibodies, they've always been very safely low.
In case I don't convert T4 to T3, we've kept the T3 dose the same for now. (Seeing that was the original problem.) If I'm converting it, I think I'll get what I can from T4 and just top up a little with T3. Although the doctor says that NDT is the best choice for the majority of people so I might end up switching and trying that. The T3 is ridiculously expensive, it's about £250 for 2-3 months supply. Compared to £17 for levo!! I'm definitely not feeling over-treated yet but it can take some weeks for that kind of thing to happen...
Whatever the heck is going on, I'm now convinced this is totally thyroid and not estrogen-related. Well, estrogen did play a role in causing this: I think my thyroid has been struggling for years as that's how long my cold feet and hands, slow metabolism, constipation, and putting weight on whilst eating ridiculously little has been going on. (I'm not overweight, but that's because I'm so stubborn and would just fast if I gained weight. In the long run, this has made everything worse for the reasons outlined here. But it was the only way to not gain weight, when you're basically eating an apple a day or something and still gaining weight...). So - all that has been going on for many years. But I just thought it was just 'me' and that's how I was. (Dur.) And any tests at the doctors where they would only test TSH and Free T4 were always fine....
Then I hit peri-menopause and started estrogen, testosterone and progesterone - and my poor thyroid couldn't deal with the increased metabolic demands of all that. (I'd been on desogestrel for 10 years due to endo, which had kept all my hormones low.) And that's when I got the symptoms and crashed. So - HRT played a role here, but it wasn't really the cause of it. I'm pretty sure that's what's going on. The only thing which has had any impact on my symptoms, is thyroid meds. Taking T3 originally and now, adding in the T4 as well. It's not all perfect yet, but it's SO MUCH better. I think in itself, that is proof that what I have going on, is thyroid.