Do I need to know my t3 and t4?: Hey I've had an... - Thyroid UK

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Do I need to know my t3 and t4?


Hey I've had an underactive thyroid for over a year now and take 25 and 50 of levo on alternate days. I went to the doctors as I wasn't feeling to good, weight gain, pains and tiredness but my results came back normal , my TSH was 1.83 , this was the only result I got as my doctors don't test T3 and T4 and says they are not worried about referring me to see a endocrinologist even though many people have recommended it to me, just looking for some ideas on whether I have anything to even be worried about or not, thank you

1 Reply

Yes you do Saffron. Doctors just don't seem to understand that TSH is a pituitary hormone and of no consequence once on thyroid meds. FT4 and FT3 are needed. FT4 to see how much free thyroxine is in your blood, and FT3 to see if T4 is converting to T3 well enough, T3 being the active hormone which every cell in our bodies need.

In a treated hypo patient generally TSH should be around 1 or below and FT4 and FT3 in the upper part of their respective reference ranges. See Treatment Options on ThyroidUK's main website where Dr Toft (leading endocrinologist and past president of the British Thyroid Association) states in Pulse Onine Magazine

"The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l. Most patients will feel well in that circumstance.

But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."

If you would like a copy of the article to discuss with your GP, email

Ask your GP to test

Vit D




Most of us Hypos have low levels and they all need to be optimal, not just in range, for thyroid hormone to work properly.

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