Hashi's causes low thyroxine, not high. Irritability and anger are FAR more common with excess thyroxine as it drives your metabolism so fast. Hashi's is more likely to cause brain fog, memory loss, dopeyness, diffculties "finding the right word" when speaking, forgetting PIN's, phonenumbers, that sort of thing. BUT if he's the sort of person who is enraged when he makes mistakes then yes, it could be the hashi's.

Hashi's people just get thyroxine too. It's autoimmune but because they can replace the thyroxine they don't bother with steroid treatment, thankfully. The tests he's not going for are just to check his antithyroid antibody levels so they can write "Hashimotos" on his notes. It doesn't change his treatment but it might be useful to get a full diagnosis to rule other stuff out. I was hoping i had post partum thyroiditis and wouldn't need meds but the antibody test confirmed it was Hashis and here to stay. In all likelihood your DH will need his bloods checked in a few weeks/months anyway to make sure his thyroxine replacement dose is doing the job. They can take his antibody test bloods then since the needle will already be in his arm.