Thyroid UK
82,636 members97,666 posts

Confused about T4 ranges

I have been on 100 mcg Levothyroxine since December for Hashimoto's Disease.

My results in December were TSH 13.7 and T4 14.

In January my results were TSH 0.5 and T4 20.

In April my results are TSH 0.9 and T4 21.7

The latest April results are from my GP and their range for T4 is 12.00-22.00. I thought that having my T4 at 21.7 would be an issue but on the results it says normal. I also saw a private doctor last year and their range is 10.00 to 28.00 for T4. I'm a bit confused by which range is correct.

Also I have been seeing a fertility doctor regarding immune issues and conceiving and he suggested going down to 75 mcg after seeing my latest results.

I'm not sure what to do but I have had a bit of a racing heart recently and have found it difficult to concentrate.

Any advice would be great.


3 Replies

Hi Lblair. 

Lab reference ranges vary which is why you are seeing different ranges with your results. For example in my experience when we moved from Somerset to Gloucestershire the labs were different hence a different reference range. This is why it is important when posting on here and in discussion with the medical profession to state the reference range with the results otherwise you could end up over or under medicated.

With regards to reducing your medication your TSH and FT4 results do no appear to be over medicated although your FT4 is getting very near the top end of optimal, i dont think i would reduce to 75mcg a day though, perhaps you could try 75mcg one day and 100mcg the next day and see how you go with that if you are feeling slightly over medicated? Im not however medically qualified to suggest what you do i am only responding with what i would or might do. Its a pity the lab didnt test your FT3 as well as this will give a better picture.

1 like

Thanks so much for your advice, it all makes sense. I thought about trying 75 one day and 100 the next myself. I will give it a go and ask my GP for a T3 test.


Thank you for your advice. I will ask for a T3 test. 


You may also like...