Free T3 and Free T4 - fasting before testing best?

Hi, going to see GP today to ask for a referral to an endocrinologist - the endocrinologist wants my free T3 and T4 to be tested prior to my seeing them - is that a good sign? What exactly are free T3 and T4? Am I right that it is best to fast prior to any thyroid tests? Can anyone recommend a good thyroid book where I can get sine more in depth information. 

Thanks so much for your help in advance, 


3 Replies

  • Is the NHS test or private one? 

    If need to organise private one see thyroid Uk for more info

    NHS rarely does FT3 test - even if requested by GP - which one reason so many here get private tests done 

    Blue horizon - thyroid plus ten blood test - easy to do at home - will check all your thyroid levels, including antibodies (which is Hashimotos) plus also checks B12, folate and ferratin - theses are often low if have thyroid issues and need to be at top end of normal range 

    Also important to check Vit d levels - see Thyroid UK 

    Blood test ideally as early as possible (8am) DON'T take any thyroid medication in 24 hours before hand (take normal dose after blood test) - also no food or drink before test - but can drink water 

  • Wennieflower, arrange early morning fasting tests (water only) as TSH may be measured in addition to T4 and T3.

    TSH is a pituitary hormone which responds to thyroid hormone levels (T4 and T3).  TSH is high when T4 and T3 are low and TSH drops when T4 and T3 are sufficient.

  • Thank you everyone - they are NHS bloods - having them done at 8.30am (earliest appointment possible). I'll only drink water! Thank you, Wennieflower 

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