I found out that my dog was hypo (low on iodine), only because I asked for a copy of the tests they had done.
Of course when you get aware of something like that all the sudden you keep seeing this mentioned in other research.
Our dog died of old age (14) but it certainly made the end of his life better.
We got a rescue dog and had them do a base test but I had to ask for the thyroid. He was fine though for me a little bit low so every few days I put a drop of Iodine in his water for maintenance.