I know there are blood tests that detect the antibodies that cause Graves - there are 2 different antibodies that are often present with Graves, but I get them confused with the ones that cause Hashimotos.
I'm trying to remember if my scan told my docs I had Graves, or if it just told them how hyperthyroid I was (very!). That was 3 years ago. Do you know if you had any of the antibody tests?
9 years ago I was diagnosed with hyperthyroidism. My GYN did blood work on me and found this out at her appt. She referred me to an ENDO Dr. He had to immediately put me on tapazole. I went to him every 2 or 3 weeks to retest me. After about 1 month my hyper turned to hypo so he had to put me on Synthroid. Then he had me taking them both until everything leveled out. Now I'm not on thyroid meds but had to go every 6 months to get retested for years. I was probably on the meds for 3 years, I had a huge goiter that disappeared. Now I have a benign nodule that has to be removed. I had a biopsy last year and it sure hurt. Now the Dr. just wants to have it removed because it's causing me pain and causing me problems swallowing.
Usually hyperthyroidism is caused by Graves or Toxic Nodules (aka Plummers). But I don't think a scan can determine Graves; I think only an Endo can determine that by other factors (of course, I'm not entirely sure I'm correct in this). I have Toxic Nodules, 3 of them, and naturally I'm hyperT, but these are easy to see on a scan, as opposed to Graves. Hopefully someone with Graves will answer you back as well and shed some more light on how it's diagnosed. I don't really know what else would be causing your hyperthyroidism.