Thyroid UK
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Maybe a "how long is a piece of string" question, but how much of the T4 in levothyroxine is converted into T3?

Obviously it depends on how well one converts the T4 to T3, but when I did the 24 hour urine test when I was taking just levo. it showed I was converting reasonably well so I wondered if there is a way of calculating what percentage of the T4 would in fact be converted.

The reason I ask is I am presently taking 1.5 grains NDT and cannot increase as I get a reaction, but I still do not feel right. My T3 is at a good level but my TSH is 1.5 and T4 below bottom of the range, so I have been pondering for a while to add in some T4.

Results 10th Jan 2017

TSH 3.2 range 0.35 - 4.7

T4 6.8 range 7.8 - 21.0

T3 5.1 range 3.8 - 6.0

Doctor agreed to re do because of TSH

Results 2nd Feb. 2017

on the same dose of NDT.

TSH 1.5

T4 6.5

T3 5.2

same ranges as above.

Last dose of NDT taken 17 hours before test and I fasted for 10 hours on both lot of tests.

When antibodies were tested at G.P. when first diagnosed nearly seven years ago I was told by G.P. I did not have the autoimmune type and said the level was 58 range 0 - 75

A.B. tested by Blue Horizon August 2015

thryoidperoxidase abs 27.5 <34

thyroglobin abs 95.4 <115

On another forum someone commented that although my anti bodies are in range, Hashi's could not be ruled out as they are very high in range, so not quite sure if I have Hashi's or not, so for this reason I have not cut out gluten.

Looking at my recent thyroid levels could anyone advise the best way forward.

Does anyone know how to work out how much T4 to add to the NDT so as not too bring my T3 over range, OR how much T4 to add to a reduced dose of NDT (and how much should the dose of NDT be reduced)

Sorry I know it maybe an impossible question to answer but I am due to go on holiday in four weeks and I am worried I may make myself worse.

Any advice really appreciated, thank you.

6 Replies

This question is impossible to answer unless you have no thyroid left at all.. The thyroid makes some T3 direct and the body tops this up by T4 conversion. Its also very difficult if you are taking NDT which is a T4/T3 mix. You need to know the ratio of T4 to T3 in NDT and compare this with the ratio in your blood but it will be a tricky calculation. Adding T4 is also a "suck it and see" trial and error and it's difficult to know what the conversion response will be to extra T4.


Many thanks Diogenes,

It was just wishful thinking on my part, that someone may come up with a "oh you can take this X amount of T4 and it will convert to Y amount of T3" but I now realise it was an impossible question to ask.

Do you mind me asking in your opinion, from looking at my antibodies, would I be classed as having Hashi's?

Thank you.

1 like

Doubtful and v early if you have.


Many thanks.


They would have to be in the thousands, I think.


Thank you.


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