A month or so ago I paid £146 for a DIO2 genetic test from Regenerus Labs regeneruslabs.com/
It confirmed exactly what I had thought for many years - that I have a genetic fault where my body cannot convert T4 into T3. It was a lot of money for me but I saved up over 2 months and it has been worth every penny. It's a saliva test so it's easy to keep spitting into a glass tube. I really urge everyone who feels unwell on T4 to get this test then you know for sure what is happening.