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Thyroid UK
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Hashimoto's; Suddenly high TSH AND high FT4?

Hi all,

it's been a while since I've been here. I've got Hashimoto disease and I've been treated for 3 years now by a endocrinologist. I need to get my blood checked every 3 months, mostly because my levels keep going up and down. I must say I also have a pituitary tumor, I've got a prolactinoma for which I get treated as well (other pituitary functions were tested and were normal).

This summer I felt unwell and when at the endocrinologist my levels seemed a bit strange:

TSH 4,0 (range 0,3-4,6)

FT4 17,4 (range 10-23)

Normally my TSH and FT4 react normal when I adjust my dose, when I feel hyper my TSH will be (too) low and visa versa. Because I felt unwell and the TSH was high we upped my dose. Three months later this are the results:

TSH 4,5 (range 0,3-4,6)

FT4 23 (range 10-23)

This is very strange to me. Normally with this FT4 results I would feel unwell and have hyper symptoms and my TSH would be too low. Right now I feel unwell but I don't have any hyper symptoms I would normally have. I feel more hypo.

I've discussed this with my endocrinologist and he said indeed it was strange and probably my body needs/wants more FT4 (why suddenly??) but we couldn't up my dose because my FT4 would get too high. He said to come back in december and check my bloods then.

As you can imagine I feel sick and waiting till december is way too long for me. So I've called and can get my blood checked next week and my doctor will call me with the results.

I always get my blood drawn at the same time (early in the mornings when the lab opens) and without levo, I take this after my blood is drawn.

My two questions;

- What if it is still the same; high TSH and high FT4? If my endocrinologist doesn't know what to do, what blood tests can I ask for? I was thinking FT3 as well (maybe the conversion is what's going wrong here?)

- What can be the cause of this? I can't find much on Google.

5 Replies

He will have to check your Free T3. That's the most important test, rarely checked.

It looks to me, and am not medically qualified that you may not be converting T4 to T3. That is what it is supposed to do. Levothyroxine T4, is inactive, it has to convert to T3. T4 is an inactive hormone and is supposed to convert to T3

I'd get a private Free T4 and Free T4 and Free T3 blood test.

Read on the link below why we need FT4 and FT3 (not the same as T4 and T3).


1 like


Whenever we see results which do not make sense, we need to think through the various possibilities which include:

Interference with the tests - e.g. from other medicines or supplements such as biotin, or antibodies to TSH.

Effect of supplements and/or other medicines on the actual TSH and/or FT4 levels.

But in your case it could make sense that the TSH is too high (e.g. an effect of something happening in your pituitary - the prolactinoma also affecting TSH production - a TSHoma) which is signalling your thyroid to produce/release thyroid hormone even though you already have sufficient thyroid hormone in your bloodstream.

Yes, I do think you should have an FT3 test as well.

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Thanks, I will ask for FT3 test if it's still the same.

I do take vitamin B12 and vitamin D supplements but I take this in the evening to make sure it can't interfere with the levo.


Have u gotten to the bottom of your question Flower3? As i am in the same boat as u my tsh and ft4 are both high and my ft3 is only middle range...


Not yet. We've waited again 3 months and that was two weeks ago. Then again high FT4 (without any hyper symptoms) and high TSH.

Because this was the third time my doctor agreed to test the FT3 as well next time. If this is low I can add T3. I've got a great doctor, he said I can try either way with T3 if I want that.

He said most people don't have any benefits with adding T3 but some do. So I will get a blood test in two months, check FT3 and if it isn't in the upper range I want to try adding T3.

Your body needs to convert the FT4 into FT3, to be able to do this your body needs some vitamins and minerals. So maybe if you have a good doctor you can ask to check for that OR try adding T3.


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