Thyroid UK
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What causes hyper symptoms - raised T3 or raised T4?

People refer to T4 to T3 conversion issues when blood tests show TSH and FT4 within range but T3 is low and this can be why hyPO symptoms remain. However, if TSH is low and FT4 is high this is indicative of being hyPER or overmedicated. If FT4 is high, will FT3 also be high? Which cause the hyper symptoms? I hope that makes sense!

12 Replies

I had conversion issues but my TSH was mid range, T4 was just over range and T3 was just under. I think generally T4 needs to look as though it is "backing up" when one us not converting. As for which causes hyper, well I guess it is the T4. The pituitary would sense plenty of hormone in the blood and so TSH would be low. From that I assume conversion of T4 to T3 would be reduced. I am sure someone will come along to clarify that! Sorry I cannot be more sure. x


Thanks. I had total thyroidectomy 10 years ago and survived for many years on 100mcg thyroxine. I have never really had hypo symptoms and so assume never had a conversion issue. I have however had blood results that indicated I was overmedicated and also had most of the things listed on the info leaflet also suggesting I was overmedicated. Levothyroxine was reduced and I appear to function well at the lower level. I am waiting on latest blood test results.

I have never had T3 tested and am really just curious as to how it fits in the equation. The guidelines from the clinical bio-chemists suggest that when TSH is below the reference range and FT4 is above, then FT3 should be tested to check for a diagnosis of some form of hyperthyroidism. That is what made me wonder if it is the T3 that causes the hyper symptoms. Quite difficult to get your had round it all. :-)


My son's results t4 18 , tsh 11.5 does this mean a conversion problem ?


I don't think so, just that he's possibly hypothyroid


What medication is your son on and what dose? No, I would not imagine he has a conversion problem. His TSH seems high but without reference ranges, cannot be sure. He might need a higher dose, unless he has only just started taking medication. I suggest you ask your GP for the ranges and post again here. How is he feeling, what is his history? Tell us more next time please. xx


I will post again in a new thread sorry did not mean to muscle in on tin lizzy post


the bottom answer is that you do not know what causes your hyper symptoms, certainly the bloods will not tell you.

you could have hyper symptoms and still be UNDER medicated for example, for a variety of reasons (ie adrenal fatigue, your body not being able to cope with T4/levo replacement like in my case, low iron and on and on and on...)

you could have bloods over and above the range and not be hyper or bloods in range and be hyper!

that is why the blood is not telling you what gets inside your cells and makes them over-work

having a suppressed TSH is not a sign/proof of being hyper either.

it is through careful/systematic/thorough assessment of your WHOLE body systems/signs/symptoms and going through a very thorough process of elimination that you will find an answer.

sounds difficult? that's why it is difficult, that is why NHS GPs far prefer to look at the blood test results and say you are hyper if they are above range or TSH is suppressed, as that takes NO EFFORT or knowledge whatsoever on their behalf, box ticked, out of the way, job done (for them not for us!!!) and if you are in pain you can be put in the fibromyagia box and if you are sad and fat you can have an anti-depressant pill and a free gym membership!


Thanks nobodysdriving. I am fortunate that my GP not only looks at the blood test results but says that how I am feeling is important. At one point he was willing to let me stay on a higher dose despite the blood test results. It was how I was feeling that led to the reduction in dosage. I have also had all the recommended vitamin, mineral, iron, liver and kidney function tests done on his suggestion, not mine and everything showed well up into optimum levels that people on this site recommend, e.g. ferritin = 113.7 (14-186) and VitB12 = 583 (190-900). As I mention above T3/FT3 is about the only one I've not had done.

I appreciate that many people have a much more difficult time than I have had and also that we need to find out what works best for us as individuals. Thanks for taking time to reply.


'A free gym membership' lol haha if you got the energy. I will start new thread ok


Sorry tin lizzy , muscled in a question on your post.

It's all baffling this.


Hi twinks, no problem. I've been away for a couple of days and not checking. Hope you got the answers your looking for. Liz




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