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Thyroid UK
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Could someone clarify T4 / T3 levels pls?

My last blood tests showed

TSH 0.9 ( 0.2-5.5)

T4 14.5 ( 10-24.5)

Serum Free ( T3 ) 4.2 ( 3.9-6.7)

I still feel exhausted on increased 75mcg from 50mcg levo.

Should both the T4 and T3 be at the top of their ranges for bests effect? Have to talk to doc tomorrow, and just wondering what to suggest next......and I'm getting a bit confused !!!!

Many thanks! :)

3 Replies

Your T3 is very low in range. You can afford to increase your thyroxine until your T3 is much higher in the range. It is fairly important that it doesn't go over the range though.

TSH is not the best measure of whether you are on the right dose and there has been recent research to back this up. It seems, according to many experts in the field (including Dr Anthony Toft) that T4 should be at the top of the range and T3 should be in the upper half of the range at least. In some cases, when patients are taking levothyroxine only, T4 needs to be slightly above range (with T3 within range) for the patient to be properly well.

I hope that helps. 75mcg is still a fairly low dose.

Carolyn x


I think people on T4 only often find that they need their FT4 to be top of the range and their FT3 to be quite high up in the range.

On a mixture of T4 and T3, I personally have found that I am better with FT3 quite high in the range but T4 only mid range - I think when I have it higher it converts to rT3. However, I think others need both to be high in the range.

Both of your FT3 and FT4 are low in the range, so I would ask for an increase in thyroxine. Hopefully you can persuade your doctor to be guided by your FT3 and FT4 levels, rather than TSH. I have managed this with mine :D xx


Thanks for that- the endo will not prescribe combination ( ie T3 ) whilst the levels are like this, i.e 'normal' , but the Dr has agreed to increase levo again to 100mcg - hoorah! She seems to be listening to me, and has indicated that she doesn't mind if the TSH ( I know, I know... :) ) gets to a suppressed level. She wrote a prescription straight away, another blood test in 6 weeks- so lets see if I get any results on the next level!


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