Thyroid UK
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High FT4 result

I had blood test this morning and GP has just phoned to tick me off and say my FT4 result is 46.

I know last time it was 10.6 in June. She has said it is very dangerous and I must see endo.

I moved in March and have been feeling very well up until July when my mother moved three doors away. So, although I am stressed, I have to say that I feel very well. I decreased my carbimazole from 30 down to 20 for two months and then down to 10 as I was falling asleep the moment I sat down in the day. I won't know my other results until they are in next week. The goiter in my neck is very much reduced and I can even say that at 57 I have a scraggy neck (which is very good really:)). So, what I am asking is should I be worried and be upping my carbimazole?

3 Replies

PingPong, yes you should be worried, FT4 46 is more than double the top of normal range. Long term undertreated hyperthyroidism can lead to atrial fibrillation and osteoporosis.

You need to resume 30mg Carbimazole until your FT4 is 20-22. It may then be possible to reduce dose to 20mg but thyroid levels should be checked 4-6 weeks after a dose reduction to check levels aren't rising.

If you're going to change the doseprescribed and your GP won't do the blood tests you can monitor levels by ordering private thyroid tests from Blue Horizon or Genova via


Thank you Clutter. Thereby lies the problem, it would have been much easier to have checked if the blood test was available every 4 to 6 weeks but GP said 12 weeks! Fortunately, at the moment, I have none of the rapid heartbeat, anxiety problems I have encountered before. I will get straight back up to 30mg a day and fingers crossed. I so would prefer not to involve endo again - you get a five minute appointment and they dictate what you will do.


Pingpong, self monitoring kinda goes with self medicating, particularly with Carbimazole where a small dose adjustment can have dramatic results. You're lucky not to be symptomatic with FT4 46.


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