
I've just gone down this road, and like Dawn says insist your vet does the Full Thyroid panel, T4, T3, Free T4 and Free T3 and antibodies for both T4 & T3
Again try checking out my post on Cushing disease, about the Immune Yahoo group, web details on there, if it hadn't of been for this group and insisting that I make sure my vets do the full panel, the vet would have never have treated my girl for Hypo T, had 3 tests done over here in the UK and my vet still didn;t believe my girl had Hypo T when the results showed differently, I eventually sent my girls bloods off to Jean Dodds in America, and Jean was so shocked about how low the readings were, she even telephoned my vet to complain about not administering the Soloxine meds. Even the skin dermotologist agreed that my girl had Hypo T even when my local vet disagreed, and it was my vet that refered us...LOL
I now have my girl on twice daily Soloxine which she will need for life.
Heres a good website that explains more about Hypo T. http://www.marvistavet.com/html/body_hypothyroidism.html
Sorry this is so long, but I hope it helps